fix DatetimeIndex.tz_localize examples docstring
[DatetimeIndex.tz_localize](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DatetimeIndex.tz_localize.html#pandas.DatetimeIndex.tz_localize) doc string has improperly formatted examples near the bottom. Trivial fix, so didn't think it needed an issue or whatsnew entry, but happy to add if needed. Now looks like:

<img width="765" alt="Screen Shot 2019-08-30 at 12 55 16 PM" src="https://user-images.githubusercontent.com/4383303/64048047-73e31080-cb25-11e9-9266-ef721bc2600b.png">


- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Thanks!