fix typo. \var vs \variable

Doc/lib/libtokenize.tex

@@ -74,7 +74,7 @@ This is useful for creating tools that tokenize a script, modify
 the token stream, and write back the modified script.
 
 \begin{funcdesc}{untokenize}{iterable}
-  Converts tokens back into Python source code.  The \variable{iterable}
+  Converts tokens back into Python source code.  The \var{iterable}
   must return sequences with at least two elements, the token type and
   the token string.  Any additional sequence elements are ignored.