golint fix (#13613)

testlib/doc.go

@@ -1,5 +1,5 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-// testlib exposes helper methods for running unit tests against a containerized test store.
+// Package testlib exposes helper methods for running unit tests against a containerized test store.
 package testlib