removed `.btn-flat` from `add-new-event`-btn in calendar demo

pages/calendar.html

@@ -658,7 +658,7 @@
                     <input id="new-event" type="text" class="form-control" placeholder="Event Title">
 
                     <div class="input-group-append">
-                      <button id="add-new-event" type="button" class="btn btn-primary btn-flat">Add</button>
+                      <button id="add-new-event" type="button" class="btn btn-primary">Add</button>
                     </div>
                     <!-- /btn-group -->
                   </div>