Fix DeprecationWarning: invalid escape sequence in versioneer.py
Hello,

This is a little patch to fix a `DeprecationWarning: invalid escape sequence` in `versioneer.py`.

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @BoboTiG! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on January 05, 2019 at 15:37 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=h1) Report
> Merging [#24636](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cb31b2b0912c99e40b22a26e598e640548ea8f14?src=pr&el=desc) will **decrease** coverage by `49.37%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24636/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #24636       +/-   ##
===========================================
- Coverage   92.38%      43%   -49.38%     
===========================================
  Files         166      166               
  Lines       52395    52395               
===========================================
- Hits        48403    22534    -25869     
- Misses       3992    29861    +25869
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `43% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.37%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-95.46%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.17%)` | :arrow_down: |
| [pandas/io/sas/sas\_xport.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfeHBvcnQucHk=) | `0% <0%> (-90.15%)` | :arrow_down: |
| [pandas/core/tools/numeric.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvdG9vbHMvbnVtZXJpYy5weQ==) | `10.44% <0%> (-89.56%)` | :arrow_down: |
| ... and [124 more](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=footer). Last update [cb31b2b...4790787](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=h1) Report
> Merging [#24636](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cb31b2b0912c99e40b22a26e598e640548ea8f14?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24636/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24636      +/-   ##
==========================================
- Coverage   92.38%   92.37%   -0.01%     
==========================================
  Files         166      166              
  Lines       52395    52379      -16     
==========================================
- Hits        48403    48386      -17     
- Misses       3992     3993       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (-0.01%)` | :arrow_down: |
| #single | `43.01% <ø> (+0.01%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals/construction.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2NvbnN0cnVjdGlvbi5weQ==) | `95.93% <0%> (-0.75%)` | :arrow_down: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `97.85% <0%> (-0.17%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88% <0%> (-0.1%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `99.34% <0%> (-0.03%)` | :arrow_down: |
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `98.51% <0%> (-0.02%)` | :arrow_down: |
| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `93.87% <0%> (ø)` | :arrow_up: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.92% <0%> (ø)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.62% <0%> (ø)` | :arrow_up: |
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `94.36% <0%> (ø)` | :arrow_up: |
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `95.41% <0%> (ø)` | :arrow_up: |
| ... and [9 more](https://codecov.io/gh/pandas-dev/pandas/pull/24636/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=footer). Last update [cb31b2b...16a51c4](https://codecov.io/gh/pandas-dev/pandas/pull/24636?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. ping on green. thanks!
