Bump httplib2 from 0.18.0 to 0.19.0

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.18.0 to 0.19.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@v0.18.0...v0.19.0)

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

Author: dependabot[bot]

requirements.txt

@@ -31,7 +31,7 @@ googleapis-common-protos==1.51.0
 grpcio==1.28.1
 h2==2.6.2
 hpack==3.0.0
-httplib2==0.18.0
+httplib2==0.19.0
 hyper==0.7.0
 hyperframe==3.2.0
 identify==1.4.7