Bump pip-tools from 5.5.0 to 6.0.0

Bumps [pip-tools](https://github.com/jazzband/pip-tools) from 5.5.0 to 6.0.0.
- [Release notes](https://github.com/jazzband/pip-tools/releases)
- [Changelog](https://github.com/jazzband/pip-tools/blob/master/CHANGELOG.md)
- [Commits](jazzband/pip-tools@5.5.0...6.0.0)

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

requirements.txt

@@ -225,7 +225,7 @@ pillow==8.1.0
     #   easy-thumbnails
 pip-chill==1.0.1
     # via -r requirements.in
-pip-tools==5.5.0
+pip-tools==6.0.0
     # via -r requirements.in
 pluggy==0.13.1
     # via pytest