Fix foreign key name for oauth_client_metadata rollback

Author: jkazimir

src/migrations/2013_08_07_183636_create_oauth_client_metadata_table.php

@@ -38,7 +38,7 @@ public function up()
     public function down()
     {
         Schema::table('oauth_client_metadata', function ($table) {
-            $table->dropForeign('oauth_grant_scopes_client_id_foreign');
+            $table->dropForeign('oauth_client_metadata_client_id_foreign');
         });
         Schema::drop('oauth_client_metadata');
     }