Fix mako syntax in rubric template.

lms/templates/combinedopenended/combined_open_ended_results.html

 <%! from django.utils.translation import ugettext as _ %>
-% num_results = len(results)
+<% num_results = len(results) %>
 % for (i,result) in enumerate(results):
     % if 'task_name' in result and 'result' in result:
         <div class="combined-rubric-container"