Contao Composer Fatal Error JSON Schema

Fatal error: Uncaught exception Composer\Json\JsonValidationException with message „./composer.json“ does not match the expected JSON schema thrown in phar://composer/composer.phar/src/Composer/Json/JsonFile.php on line 183

Troubleshooting:
http://github.com/contao-community-alliance/composer-client/issues/300

Open file composer.json

Change:
„url“: „https?://legacy-packages-via.contao-community-alliance.org/“  to
„url“: „http://legacy-packages-via.contao-community-alliance.org/“