Bump pillow from 5.1.0 to 6.2.0 (#54)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.1.0 to 6.2.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@5.1.0...6.2.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -7,7 +7,7 @@ djangorestframework==3.8.2
 gunicorn==19.9.0
 idna==2.6
 numpy==1.14.5
-Pillow==5.1.0
+Pillow==6.2.0
 psycopg2==2.7.5
 pytz==2018.4
 redis==2.10.6