Fixing flake8 problems new to flake8 3.6.0
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Seems like flake8 3.6.0 has just been released to conda. And when the CI uses the new version, it fails on the linting because a new validation `W605` which checks invalid escape characters. We have few in scripts and the conf of the documentation. Fixing those, so CI passes again.

Hello @datapythonista! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`doc/source/conf.py`](https://github.com/datapythonista/pandas/blob/9a5f5b6b57697a96ef0353e4fefc624d6a8e7b48/doc/source/conf.py) !

 - There are no PEP8 issues in the file [`scripts/find_commits_touching_func.py`](https://github.com/datapythonista/pandas/blob/9a5f5b6b57697a96ef0353e4fefc624d6a8e7b48/scripts/find_commits_touching_func.py) !

 - There are no PEP8 issues in the file [`scripts/find_undoc_args.py`](https://github.com/datapythonista/pandas/blob/9a5f5b6b57697a96ef0353e4fefc624d6a8e7b48/scripts/find_undoc_args.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23472?src=pr&el=h1) Report
> Merging [#23472](https://codecov.io/gh/pandas-dev/pandas/pull/23472?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f7f0c597f34dd7346ed736f3c588b32c35dd1556?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23472/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23472?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23472   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         161      161           
  Lines       51187    51187           
=======================================
  Hits        47209    47209           
  Misses       3978     3978
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.61% <ø> (ø)` | :arrow_up: |
| #single | `42.26% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23472?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/23472?src=pr&el=footer). Last update [f7f0c59...9a5f5b6](https://codecov.io/gh/pandas-dev/pandas/pull/23472?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @datapythonista nice that these are now being caught in flake