Bump cachetools from 3.1.1 to 4.0.0 (#301)

dependabot-preview[bot] · web-flow · commit 5894e96e1737 · 2019-12-16T05:44:15.000Z
diff --git a/requirements.txt b/requirements.txt
@@ -1,7 +1,7 @@
 cherry_picker==1.3.2
 aiohttp==3.6.2
 gidgethub==3.2.0
-cachetools==3.1.1
+cachetools==4.0.0
 redis==3.3.11
 celery==4.3.0
 sentry-sdk==0.13.5
