update meta doc

Author: goetas

META.md

@@ -3,5 +3,5 @@
 Use: https://github.com/skywinder/Github-Changelog-Generator
 
 ```bash
-github_changelog_generator --username=schmittjoh --project=serializer --pull-requests --no-compare-link -t GITHUB-TOKEN
+github_changelog_generator --user=schmittjoh --project=serializer --pull-requests --no-compare-link -t GITHUB-TOKEN
 ```