Bump pillow from 5.1.0 to 6.2.0 (#371)

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](https://github.com/python-pillow/Pillow/compare/5.1.0...6.2.0)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: Arona Jones <aj@aronajones.com>

requirements.txt

@@ -18,7 +18,7 @@ gunicorn==19.8.1
 icalendar==4.0.1
 lxml==4.2.1
 Markdown==2.6.11
-Pillow==5.1.0
+Pillow==6.2.0
 psycopg2==2.7.4
 Pygments==2.2.0
 PyPDF2==1.26.0