Bump httplib2 from 0.9.2 to 0.19.0 in /backwork

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.9.2 to 0.19.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@0.9.2...v0.19.0)

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

Author: dependabot[bot]

backwork/requirements.txt

@@ -1,5 +1,5 @@
 contextlib2==0.5.4
-httplib2==0.9.2
+httplib2==0.19.0
 backwork==0.3.0
 backwork-backup-files==0.3.0
 backwork-backup-mongo==0.3.0