Fix incorrect variable reference in code example for documentation.
Fix incorrect variable reference in code example for documentation.

ionelmc/python-lazy-object-proxy,pombredanne/python-lazy-object-proxy,pombredanne/python-lazy-object-proxy,wujuguang/wrapt,GrahamDumpleton/wrapt,wujuguang/wrapt,github4ry/wrapt,GrahamDumpleton/wrapt,linglaiyao1314/wrapt,github4ry/wrapt,ionelmc/python-lazy-object-proxy,pombredanne/wrapt,linglaiyao1314/wrapt,akash1808/wrapt,akash1808/wrapt,pombredanne/wrapt