Merge pull request #1020 from overleaf/msm-update-mongo-4-2

Update mongo version for upcoming CE 3.1.0 version

docker-compose.yml

@@ -103,7 +103,7 @@ services:
 
     mongo:
         restart: always
-        image: mongo:4.0
+        image: mongo:4.2
         container_name: mongo
         expose:
             - 27017