Fix typo in Motivation section header

Author: brettcannon

peps/pep-0840.rst

@@ -17,8 +17,8 @@ There is a long-standing inconsistency in the way variable names are
 resolved in classes.  Several alternatives to resolve this
 inconsistency are discussed.
 
-Movtivation
-===========
+Motivation
+==========
 
 Name resolution in a class namespace uses a partial dynamic lookup. A
 name can be either local or global depending on whether an assignment