Bump pillow from 4.2.1 to 7.1.0 (#942)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 4.2.1 to 7.1.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@4.2.1...7.1.0)

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pip-requirements-test.txt

@@ -20,4 +20,4 @@ simpletraj
 matplotlib==2.0.2
 moviepy==0.2.2.11
 imageio==1.6
-pillow==4.2.1
+pillow==7.1.0