Bump pillow from 6.2.0 to 7.1.2 in /cvat/requirements (#1690)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 6.2.0 to 7.1.2.
- [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/6.2.0...7.1.2)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

cvat/requirements/base.txt

@@ -6,7 +6,7 @@ django-cacheops==4.0.6
 django-compressor==2.2
 django-rq==2.0.0
 EasyProcess==0.2.3
-Pillow==6.2.0
+Pillow==7.1.2
 numpy==1.16.2
 python-ldap==3.0.0
 pytz==2018.3