fix underline to match the title's length

xabbuh · weaverryan · commit 29f346a030a7 · 2013-08-25T07:59:37.000-04:00
diff --git a/reference/constraints/NotIdenticalTo.rst b/reference/constraints/NotIdenticalTo.rst
@@ -1,5 +1,5 @@
 NotIdenticalTo
-===========
+==============
 
 .. versionadded:: 2.3
     This constraint is new in version 2.3.
