Update minio docker image and minio-go dependency (#10770)

* update minio server1

* update minio go lib to use the latest release

build/docker-compose.yml

@@ -25,13 +25,14 @@ services:
       POSTGRES_DB: mattermost_test
     tmpfs: /var/lib/postgresql/data
   minio:
-    image: "minio/minio:RELEASE.2018-05-25T19-49-13Z"
+    image: "minio/minio:RELEASE.2019-04-23T23-50-36Z"
     command: "server /data"
     networks:
       - mm-test
     environment:
       MINIO_ACCESS_KEY: minioaccesskey
       MINIO_SECRET_KEY: miniosecretkey
+      MINIO_SSE_MASTER_KEY: "my-minio-key:6368616e676520746869732070617373776f726420746f206120736563726574"
   inbucket:
     image: "jhillyerd/inbucket:release-1.2.0"
     restart: always