DOC: Fixed the doctsring for _set_axis_name (GH 22895)
Fixed the docstring of the function `_set_axis_name` in `pandas/core/generic.py`

Closes #22895
Hello @bkjchoi72! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/core/generic.py`](https://github.com/bkjchoi72/pandas/blob/a7eb3d8121a32119f2b0974e8b1f9234d1c6206f/pandas/core/generic.py) !



##### Comment last updated on October 09, 2018 at 08:34 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22969?src=pr&el=h1) Report
> Merging [#22969](https://codecov.io/gh/pandas-dev/pandas/pull/22969?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/deb7b4d5003b939f47e525bcdaceeea48622a73a?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22969/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22969?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22969      +/-   ##
==========================================
+ Coverage   92.28%   92.28%   +<.01%     
==========================================
  Files         161      161              
  Lines       51451    51452       +1     
==========================================
+ Hits        47483    47484       +1     
  Misses       3968     3968
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <100%> (ø)` | :arrow_up: |
| #single | `42.28% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22969?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/22969/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.84% <100%> (ø)` | :arrow_up: |

------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22969?src=pr&el=footer). Last update [deb7b4d...9d944e8](https://codecov.io/gh/pandas-dev/pandas/pull/22969?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @bkjchoi72 : FYI, you don't have to close your PR (#22968) and open a new if there are issues with it.  You can keep making commits to the existing PR and fix them there. @jreback @datapythonista Thanks for the patience guys. Let me make adjustments based on your feedback. @bkjchoi72 can you take a look at the errors in travis please? they look like genuine errors in your PR. @datapythonista The tests are fixed. Thanks for your time and guidance! did you run `flake8 --doctests pandas/core/generic.py`? I think there is a wrong indentation in your example (note that the command will show errors in other parts of the file that you can ignore). @datapythonista I don't see indentation errors related to my changes. I modified lines 1120 - 1191 and 1207 -1258. Below is the output of `flake8 --doctests pandas/core/generic.py`.
```
$ flake8 --doctests pandas/core/generic.py
pandas/core/generic.py:659:13: F821 undefined name 'p'
pandas/core/generic.py:660:13: F821 undefined name 'p'
pandas/core/generic.py:3195:13: F821 undefined name 'df'
pandas/core/generic.py:3200:13: F821 undefined name 'df'
pandas/core/generic.py:3205:13: F821 undefined name 'df'
pandas/core/generic.py:3211:13: F821 undefined name 'df'
pandas/core/generic.py:3218:13: F821 undefined name 'df'
pandas/core/generic.py:3222:13: F821 undefined name 'df'
pandas/core/generic.py:3227:13: F821 undefined name 'df'
pandas/core/generic.py:7545:71: F721 syntax error in doctest
pandas/core/generic.py:7548:13: F821 undefined name 's'
pandas/core/generic.py:7556:13: F821 undefined name 's'
pandas/core/generic.py:7567:13: F821 undefined name 's'
pandas/core/generic.py:7599:52: F721 syntax error in doctest
pandas/core/generic.py:7603:13: F821 undefined name 'df2'
```
None in the range that I modified shows up from my end. Do you have specific line numbers that are violating pep8 standards? Sorry for the delay @bkjchoi72, can you fix the conflicts, so we can merge? @bkjchoi72, do you have time to fix the conflicts? @datapythonista I'll get to it this weekend. Rebased, and added some more fixes to the docstring.

@Dr-Irv @jreback can you take a look? thanks @bkjchoi72  @datapythonista I was on vacation for the past 10 days, so just saw this now.  All looks good to me.