update of ChainMap docstring to conform to Numpy docstring
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @josharoon! Thanks for updating the PR.



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

##### Comment last updated on November 14, 2017 at 21:11 Hours UTC Thanks. This is an internal class that we've backported from python3. I suspect the docstring was just copied over from the standard library.

This may not be a super useful change since

- it's not included in pandas' documentation
- pandas developers would just reference the offical python docs (I think)

If you are interested in contributing to the docs, we have a bunch of known issues tagged: https://github.com/pandas-dev/pandas/issues?q=is%3Aopen+is%3Aissue+label%3ADocs
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=h1) Report
> Merging [#18289](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/63e8527d32aaf6afe1cd4b2a7b3bfadb088c9a72?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18289/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18289      +/-   ##
==========================================
- Coverage    91.4%   91.38%   -0.02%     
==========================================
  Files         164      164              
  Lines       49880    49880              
==========================================
- Hits        45591    45583       -8     
- Misses       4289     4297       +8
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.19% <ø> (ø)` | :arrow_up: |
| #single | `39.42% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/chainmap\_impl.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9jaGFpbm1hcF9pbXBsLnB5) | `0% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18289?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/18289?src=pr&el=footer). Last update [63e8527...fe8f475](https://codecov.io/gh/pandas-dev/pandas/pull/18289?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/18289?src=pr&el=h1) Report
> Merging [#18289](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/63e8527d32aaf6afe1cd4b2a7b3bfadb088c9a72?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `0%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18289/graphs/tree.svg?width=650&height=150&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18289      +/-   ##
==========================================
- Coverage    91.4%   91.38%   -0.02%     
==========================================
  Files         164      164              
  Lines       49880    49880              
==========================================
- Hits        45591    45583       -8     
- Misses       4289     4297       +8
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.19% <0%> (ø)` | :arrow_up: |
| #single | `39.42% <0%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/compat/chainmap\_impl.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9jaGFpbm1hcF9pbXBsLnB5) | `0% <0%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18289?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/18289?src=pr&el=footer). Last update [63e8527...d2b0bda](https://codecov.io/gh/pandas-dev/pandas/pull/18289?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
