Update selenium from 3.0.2 to 3.3.3

Author: pyup-bot

requirements-dev.txt

@@ -17,5 +17,5 @@ py==1.4.33                # via pytest
 pyflakes==1.5.0 # via flake8
 pytest-django==3.1.2
 pytest==3.0.7
-selenium==3.0.2
+selenium==3.3.3
 six==1.10.0               # via django-appconf