fix r local hooks

`language: r` acts more like `language: script` so we have to *not* append
the prefix when run with `repo: local`

tests/repository_test.py

@@ -48,6 +48,7 @@ def _hook_run(hook, filenames, color):
             hook.entry,
             hook.args,
             filenames,
+            is_local=hook.src == 'local',
             require_serial=hook.require_serial,
             color=color,
         )