Bump celery from 4.3.0 to 4.4.0 (#302)

dependabot-preview[bot] · web-flow · commit 61dabd3f8c10 · 2019-12-16T05:47:19.000Z
diff --git a/requirements.txt b/requirements.txt
@@ -3,5 +3,5 @@ aiohttp==3.6.2
 gidgethub==3.2.0
 cachetools==4.0.0
 redis==3.3.11
-celery==4.3.0
+celery==4.4.0
 sentry-sdk==0.13.5
