Fix i18n errors found along the way.

lms/templates/courseware/accordion.html

@@ -31,7 +31,7 @@
                     due_date = ''
                 else:
                     formatted_string = get_time_display(section['due'], due_date_display_format, coerce_tz=settings.TIME_ZONE)
-                    due_date = '' if len(formatted_string)==0 else _('due {date}'.format(date=formatted_string))
+                    due_date = '' if len(formatted_string)==0 else _('due {date}').format(date=formatted_string)
               %>
               <p class="subtitle">${section['format']} ${due_date}</p>
             </a>