Update requests from 2.19.0 to 2.19.1

Author: pyup-bot

requirements.txt

@@ -1,5 +1,5 @@
 pillow==5.1.0  # Image library.
 pytz==2018.4
 requests-mock==1.5.0  # Mock `requests`.
-requests==2.19.0
+requests==2.19.1
 wrapt==1.10.11  # Make better decorators.