CLN: add missing space in package's description
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

The typo fixed here is in the package description, so it shows up in `pip show`. I'd say this fix needs no issue or whatsnew entry; if you feel otherwise, please say so and I'll open an issue and resubmit with a whatsnew entry.

```
$ pip show pandas
Name: pandas
Version: 0.22.0
Summary: Powerful data structures for data analysis, time series,and statistics
Home-page: http://pandas.pydata.org
Author: The PyData Development Team
Author-email: pydata@googlegroups.com
[...]
```