Revert "Fixtypo."

This reverts commit 62d9a78c.

biscuit/apps/chronos/templates/chronos/lessons_list.html

@@ -22,7 +22,7 @@
    <thead>
     <tr>
      <th>{% blocktrans %}Period{% endblocktrans %}</th>
-     <th>{% blocktrans %}Groups{% endblocktrans %}</th>
+     <th>{% blocktrans %}Groups{% endblocktans %}</th>
      <th>{% blocktrans %}Subject{% endblocktrans %}</th>
      <th>{% blocktrans %}Teachers{% endblocktrans %}</th>
     </tr>