Scheduled monthly dependency update for December (#50)

* Update cachetools from 2.1.0 to 3.0.0

* Update requests from 2.20.0 to 2.20.1

* Update redis from 2.10.6 to 3.0.1

* Update requirements.txt

Author: pyup-bot

requirements.txt

@@ -1,7 +1,7 @@
 aiohttp==3.4.4
 black==18.9b0
-cachetools==2.1.0
+cachetools==3.0.0
 celery==4.2.1
 gidgethub==3.0.0
-requests==2.20.0
-redis==2.10.6
+requests==2.20.1
+redis==2.10.6