Merge pull request #1670 from antoviaque/hidden-module-unicode

hidden-module-unicode: Return unicode string to pass assertion

common/lib/xmodule/xmodule/hidden_module.py

@@ -5,9 +5,9 @@ from xmodule.raw_module import RawDescriptor
 class HiddenModule(XModule):
     def get_html(self):
         if self.system.user_is_staff:
-            return "ERROR: This module is unknown--students will not see it at all"
+            return u"ERROR: This module is unknown--students will not see it at all"
         else:
-            return ""
+            return u""
 
 
 class HiddenDescriptor(RawDescriptor):