Translatable strings are not being properly updated on devserver
## Summary

- Sometimes tr strings that are modified do not get properly updated.

## System information

 - Version: 0.6
 - Operating system: Ubuntu
 - Node 6.11.2

## How to reproduce

1. Try editing tr strings and check that they are updated in the UI. Pretty random.

## Real-life consequences 

- Development rage 
diff --git a/kolibri/core/webpack/hooks.py b/kolibri/core/webpack/hooks.py
index 257ea9c632..1d623a97e8 100644
--- a/kolibri/core/webpack/hooks.py
+++ b/kolibri/core/webpack/hooks.py
@@ -236,7 +236,7 @@ class WebpackBundleHook(hooks.KolibriHook):
     def frontend_messages(self):
         global _JSON_MESSAGES_FILE_CACHE
         lang_code = get_language()
-        if not _JSON_MESSAGES_FILE_CACHE.get(self.unique_slug, {}).get(lang_code):
+        if not _JSON_MESSAGES_FILE_CACHE.get(self.unique_slug, {}).get(lang_code) or django_settings.DEBUG:
             frontend_message_file = self.frontend_message_file(lang_code)
             if frontend_message_file:
                 with open(frontend_message_file) as f:
['kolibri/core/webpack/hooks.py']