fix flash msg for login page

tracim/tracim/templates/master_anonymous.mak

@@ -48,7 +48,7 @@
     </body>
 
 <%def name="content_wrapper()">
-    ${TIM.FLASH_MSG('col-sm-6 col-sm-offset-3')}
+    ${TIM.FLASH_MSG('')}
     ${self.body()}
 </%def>