Bump pillow from 5.3.0 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 5.3.0 to 8.1.1.
- [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/5.3.0...8.1.1)

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

requirements.txt

@@ -4,7 +4,7 @@ feedparser==5.2.1
 idna==2.7
 lxml==4.2.5
 oauthlib==2.1.0
-Pillow==5.3.0
+Pillow==8.1.1
 PySocks==1.6.8
 requests==2.19.1
 requests-oauthlib==1.0.0