DOC: update the pandas.Series.dt.is_month_end docstring
Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

- [X] PR title is "DOC: update the <your-function-or-method> docstring"
- [X] The validation script passes: `scripts/validate_docstrings.py <your-function-or-method>`
- [X] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] The html version looks good: `python doc/make.py --single <your-function-or-method>`
- [X] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

```
################################################################################
################## Docstring (pandas.Series.dt.is_month_end)  ##################
################################################################################

Return a boolean indicating whether the date is the last day of the month.

Returns
-------
is_month_end : Series of boolean.

See Also
--------
is_month_start : Return a boolean indicating whether the date is
    the first day of the month.

Examples
--------
>>> dates = pd.Series(pd.date_range("2018-02-27", periods=3))
>>> dates
0   2018-02-27
1   2018-02-28
2   2018-03-01
dtype: datetime64[ns]
>>> dates.dt.is_month_end
0    False
1    True
2    False
dtype: bool

################################################################################
################################## Validation ##################################
################################################################################

Errors found:
	No extended summary found

```

If the validation script still gives errors, but you think there is a good reason
to deviate in this case (and there are certainly such cases), please state this
explicitly.

No extended summary required in this case (as confirmed with peers).

Hello @janelle! Thanks for updating the PR.



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

##### Comment last updated on March 17, 2018 at 11:56 Hours UTC The sentences for See Also section is too long, need to break it into 2 lines. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20181?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@f7a5682`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20181/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20181?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #20181   +/-   ##
=========================================
  Coverage          ?   91.92%           
=========================================
  Files             ?      150           
  Lines             ?    50572           
  Branches          ?        0           
=========================================
  Hits              ?    46486           
  Misses            ?     4086           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.35% <ø> (?)` | |
| #single | `42.13% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20181?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/20181/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.64% <ø> (ø)` | |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20181?src=pr&el=footer). Last update [f7a5682...2b540e0](https://codecov.io/gh/pandas-dev/pandas/pull/20181?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks @janelle !