Bump httplib2 from 0.17.3 to 0.18.0 in /websocket_server

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.17.3 to 0.18.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@v0.17.3...v0.18.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

websocket_server/requirements.txt

@@ -15,7 +15,7 @@ google-auth-oauthlib==0.4.1
 googleapis-common-protos==1.51.0
 greenlet==0.4.15
 gunicorn==20.0.4
-httplib2==0.17.3
+httplib2==0.18.0
 idna==2.9
 itsdangerous==1.1.0
 Jinja2==2.11.2