Bump isort version.

tox.ini

@@ -25,7 +25,7 @@ deps=
     linkcheck,apicheck,configcheck: -r{toxinidir}/requirements/docs.txt
     flake8,flakeplus,pydocstyle: -r{toxinidir}/requirements/pkgutils.txt
     isort-check: -r{toxinidir}/requirements/test-ci-default.txt
-    isort-check: git+https://github.com/timothycrosley/isort.git
+    isort-check: isort>=4.3.1
     bandit: bandit
 sitepackages = False
 recreate = False