Bump httplib2 from 0.8 to 0.19.0

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.8 to 0.19.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](https://github.com/httplib2/httplib2/commits/v0.19.0)

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

requirements-old.txt

@@ -55,7 +55,7 @@ future==0.18.2
 gdata==2.0.18
 h5py==2.10.0
 html5lib==1.1
-httplib2==0.8
+httplib2==0.19.0
 ipaddress==1.0.17
 ipython==5.1.0
 ipython-genutils==0.1.0