Use HTTP basic authentication to API

GitHub API authentication using the `access_token` query paramater has
been deprecated[1]. Instead, use HTTP basic authentication. This
requires using a `urllib2.Request` object to supply additional headers.
In the future this code should probably switch to using `requests`.

1. https://developer.github.com/changes/2019-11-05-deprecated-passwords-and-authorizations-api/#authenticating-using-query-parameters

https://phabricator.endlessm.com/T29306