Update requests from 2.18.4 to 2.19.0

Author: pyup-bot

requirements.txt

@@ -2,5 +2,5 @@ constantly==15.1.0  # Symbolic constants.
 pillow==5.1.0  # Image library.
 pytz==2018.4
 requests-mock==1.5.0  # Mock `requests`.
-requests==2.18.4
+requests==2.19.0
 wrapt==1.10.11  # Make better decorators.