DOC: Fix read_stata docstring
- [x] passes `git diff upstream/master | flake8 --diff`

Found docstring example is broken:
- http://pandas.pydata.org/pandas-docs/stable/generated/pandas.read_stata.html

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13312?src=pr) is **84.22%**

> Merging [#13312](https://codecov.io/gh/pydata/pandas/pull/13312?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #13312   diff @@
==========================================
  Files           138        138          
  Lines         50666      50666          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          42672      42672          
  Misses         7994       7994          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [ae2ca83...a9a7357](https://codecov.io/gh/pydata/pandas/compare/ae2ca83d31ebc2f95bb4f71b504f454ec399ee41...a9a7357bf3bc9c4df9e5965324f46678a16a1e3b)
