DOC: resolved mistakes in examples series
Adjusted some docstring examples.

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15625?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@2229c26`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.


```diff
@@            Coverage Diff            @@
##             master   #15625   +/-   ##
=========================================
  Coverage          ?   90.99%           
=========================================
  Files             ?      143           
  Lines             ?    49306           
  Branches          ?        0           
=========================================
  Hits              ?    44868           
  Misses            ?     4438           
  Partials          ?        0
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15625?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/compare/2229c26442ea28b7d69819e0b52b9bbc45afae4a...32b0dc66a1d34a6a9f36ef31d429f4b7008f9314?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.25% <ø> (ø)` | |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/compare/2229c26442ea28b7d69819e0b52b9bbc45afae4a...32b0dc66a1d34a6a9f36ef31d429f4b7008f9314?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.91% <ø> (ø)` | |
| [pandas/conftest.py](https://codecov.io/gh/pandas-dev/pandas/compare/2229c26442ea28b7d69819e0b52b9bbc45afae4a...32b0dc66a1d34a6a9f36ef31d429f4b7008f9314?src=pr&el=tree#diff-cGFuZGFzL2NvbmZ0ZXN0LnB5) | `94.11% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15625?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/15625?src=pr&el=footer). Last update [2229c26...46d362e](https://codecov.io/gh/pandas-dev/pandas/compare/2229c26442ea28b7d69819e0b52b9bbc45afae4a...46d362e1dabafaefdf9d4936f40efe9ecd5a53ad?el=footer&src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). @MichielStock There were some PEP8 issues (lines too long, we test for that on Travis), but fixed those before merging.

Thanks!