Fix typo

Doc/ref/ref3.tex

@@ -1216,7 +1216,7 @@ defined to handle simple, but not extended slices.) It is also recommended
 that mappings provide the methods \method{keys()}, \method{values()},
 \method{items()}, \method{has_key()}, \method{get()}, \method{clear()},
 \method{setdefault()}, \method{iterkeys()}, \method{itervalues()},
-\method{iteritems()}, \method{pop()},, \method{popitem()},		     
+\method{iteritems()}, \method{pop()}, \method{popitem()},		     
 \method{copy()}, and \method{update()} behaving similar to those for
 Python's standard dictionary objects.  The \module{UserDict} module
 provides a \class{DictMixin} class to help create those methods