You need to change the composer.json of the project where you want to install this package. Then "minimum-stability": "dev" should work.
Also, it seems that the repo on Github is private since I can't access it ;)
If you want to test your package against a real Laravel app, you should create a release for the created package on Github. This way you can download it without modifying the composer.json. Check this: https://stackoverflow.com/questions/41149552/composer-packagist-could-not-find-package-for-minimum-stability#answer-57801073