Update isort from 4.2.15 to 4.3.0

Author: pyup-bot

dev-requirements.txt

@@ -6,7 +6,7 @@ flake8==3.5.0  # Lint
 flake8-quotes==0.13.0  # Require single quotes
 freezegun==0.3.9  # Freeze time in tests
 hypothesis==3.44.22  # Generate test cases
-isort==4.2.15  # Lint imports
+isort==4.3.0  # Lint imports
 mypy==0.560  # Type checking
 pip_check_reqs==2.0.1
 pydocstyle==2.1.1  # Lint docstrings