remove useless semicolons
Some semicolons were used without reason.

I don't think this is without reason? 
I think it supresses the output like `Out[15]: <matplotlib.axes._subplots.AxesSubplot at 0x7fc57ae70c50>` 

Still, question is if this is needed, but IMO it makes the docs a bit cleaner. BTW, something that may not be needed is actually the full `plt.figure();`, but it should be checked that it works for plotting series without that (as series.plot(..) tends to plot an the existing previous figure in an interactive environment). The semicolons that I remove were probably copy/paste mistakes omg, it's seem to be a feature... there are some hidden tricks with IPython using semicolons. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15645?src=pr&el=h1) Report
> Merging [#15645](https://codecov.io/gh/pandas-dev/pandas/pull/15645?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a703abcb6328b105bfa0b30895b8893f7f52f88f?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.


```diff
@@            Coverage Diff             @@
##           master   #15645      +/-   ##
==========================================
- Coverage   91.02%      91%   -0.03%     
==========================================
  Files         143      143              
  Lines       49324    49324              
==========================================
- Hits        44898    44886      -12     
- Misses       4426     4438      +12
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15645?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/compare/a703abcb6328b105bfa0b30895b8893f7f52f88f...30dd3f509f47129cfedf33fdc704946e09cb5549?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :x: |
| [pandas/tools/merge.py](https://codecov.io/gh/pandas-dev/pandas/compare/a703abcb6328b105bfa0b30895b8893f7f52f88f...30dd3f509f47129cfedf33fdc704946e09cb5549?src=pr&el=tree#diff-cGFuZGFzL3Rvb2xzL21lcmdlLnB5) | `91.76% <0%> (-0.35%)` | :x: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/compare/a703abcb6328b105bfa0b30895b8893f7f52f88f...30dd3f509f47129cfedf33fdc704946e09cb5549?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.96% <0%> (-0.34%)` | :x: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/compare/a703abcb6328b105bfa0b30895b8893f7f52f88f...30dd3f509f47129cfedf33fdc704946e09cb5549?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.87% <0%> (-0.1%)` | :x: |

------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15645?src=pr&el=footer). Last update [a703abc...30dd3f5](https://codecov.io/gh/pandas-dev/pandas/compare/a703abcb6328b105bfa0b30895b8893f7f52f88f...30dd3f509f47129cfedf33fdc704946e09cb5549?el=footer&src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).