Bump httplib2 from 0.12.1 to 0.19.0

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.12.1 to 0.19.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@v0.12.1...v0.19.0)

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

requirements.txt

@@ -3,7 +3,7 @@ cachetools==3.1.0
 google-api-python-client==1.7.8
 google-auth-httplib2==0.0.3
 google-auth==1.6.3
-httplib2==0.12.1
+httplib2==0.19.0
 pyasn1-modules==0.2.4
 pyasn1==0.4.5
 rsa==4.0