composer: Fix changed status

Fix `changed` status that always returns False with composer.

This [previous PR](https://github.com/ansible/ansible-modules-extras/pull/61) had fixed the issue but because of a [Composer recent change](cb336a5416) stderr is now used for reporting information meant for humans while stdout is more for the output of the command.

This PR would definilty solve this issue.

packaging/language/composer.py

@@ -159,7 +159,8 @@ def main():
         output = parse_out(err)
         module.fail_json(msg=output)
     else:
-        output = parse_out(out)
+        # Composer version > 1.0.0-alpha9 now use stderr for standard notification messages
+        output = parse_out(out + err)
         module.exit_json(changed=has_changed(output), msg=output)
 
 # import module snippets