Merge pull request #3946 from edx/anton/i18n-code-response

CodeResponse: fix i18n.

common/lib/capa/capa/responsetypes.py

@@ -1915,7 +1915,7 @@ class CodeResponse(LoncapaResponse):
         if self.capa_system.xqueue is None:
             cmap = CorrectMap()
             cmap.set(self.answer_id, queuestate=None,
-                     msg=_(u'Error checking problem: no external queueing server is configured.'))
+                     msg=_(u'Error: No grader has been set up for this problem.'))
             return cmap
 
         # Prepare xqueue request