docs: fix unescaped html tag (#802)
docs: fix unescaped html tag (#802)

If the description of the method contains any HTML tag, it will
break the HTML rendering.
This commit escapes the html tag to prevent this problem.
* Use html standard lib when using python3
* Use cgi standard lib when using python2

Refs #791

Release-As: 1.8.2
googleapis/google-api-python-client,googleapis/google-api-python-client