update minio docker image (#11905)

build/docker-compose.common.yml

@@ -21,7 +21,7 @@ services:
       POSTGRES_PASSWORD: mostest
       POSTGRES_DB: mattermost_test
   minio:
-    image: "minio/minio:RELEASE.2019-04-23T23-50-36Z"
+    image: "minio/minio:RELEASE.2019-08-14T20-37-41Z"
     command: "server /data"
     networks:
       - mm-test