fixed two typehints on migrations repository

src/Database/DatabaseMigrationRepository.php

@@ -51,6 +51,7 @@ class DatabaseMigrationRepository implements MigrationRepositoryInterface
     /**
      * Get the ran migrations.
      *
+     * @param string $extension
      * @return array
      */
     public function getRan($extension = null)

src/Database/MigrationRepositoryInterface.php

@@ -16,6 +16,7 @@ interface MigrationRepositoryInterface
     /**
      * Get the ran migrations for the given extension.
      *
+     * @param string $extension
      * @return array
      */
     public function getRan($extension = null);