Bump pillow from 6.2.0 to 8.1.2

Bumps [pillow](https://github.com/python-pillow/Pillow) from 6.2.0 to 8.1.2.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@6.2.0...8.1.2)

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

requirements/base.txt

@@ -41,7 +41,7 @@ msgpack==0.6.0
 multidict==4.5.2
 numpy==1.19.1
 pandas==0.25.1
-Pillow==6.2.0  # https://github.com/python-pillow/Pillow
+Pillow==8.1.2  # https://github.com/python-pillow/Pillow
 profilehooks==1.11.0
 PyHamcrest==1.9.0
 python-coveralls==2.9.3