Bump isort from 4.3.21 to 5.1.1

Bumps [isort](https://github.com/timothycrosley/isort) from 4.3.21 to 5.1.1.
- [Release notes](https://github.com/timothycrosley/isort/releases)
- [Changelog](https://github.com/timothycrosley/isort/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/timothycrosley/isort/compare/4.3.21...5.1.1)

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

requirements.txt

@@ -21,7 +21,7 @@ whitenoise==5.1.0
 flake8==3.8.3
 flake8-debugger==3.2.1
 flake8-blind-except==0.1.1
-isort==4.3.21
+isort==5.1.1
 
 # Helpers
 pyprof2calltree==1.4.5