Add support for author in Repositories::commits (#777)

Author: tetreum

src/Api/Repositories.php

@@ -212,6 +212,7 @@ public function commits($project_id, array $parameters = [])
 
         $resolver->setDefined('path');
         $resolver->setDefined('ref_name');
+        $resolver->setDefined('author');
         $resolver->setDefined('since')
             ->setAllowedTypes('since', \DateTimeInterface::class)
             ->setNormalizer('since', $datetimeNormalizer)