Bump httplib2 from 0.10.3 to 0.19.0

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.10.3 to 0.19.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@v0.10.3...v0.19.0)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -46,7 +46,7 @@ get==1.0.3
 google-api-python-client==1.6.3
 gunicorn==19.7.1
 html5lib==0.9999999
-httplib2==0.10.3
+httplib2==0.19.0
 idna==2.6
 ipaddress==1.0.18
 jsonpickle==0.9.5