Upgrading server dependancies (#8154)

cmd/platform/mattermost.go

@@ -21,6 +21,9 @@ import (
 	_ "github.com/go-ldap/ldap"
 	_ "github.com/hashicorp/memberlist"
 	_ "github.com/mattermost/rsc/qr"
+	_ "github.com/prometheus/client_golang/prometheus"
+	_ "github.com/prometheus/client_golang/prometheus/promhttp"
+	_ "github.com/tylerb/graceful"
 	_ "gopkg.in/olivere/elastic.v5"
 )