Bump httplib2 from 0.17.3 to 0.19.0

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.17.3 to 0.19.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@v0.17.3...v0.19.0)

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

requirements.txt

@@ -1,7 +1,7 @@
 Django==2.2.12 # pyup: < 3
 
 pytz==2020.1
-httplib2==0.17.3
+httplib2==0.19.0
 feedparser==5.2.1
 Markdown==3.2.1
 psycopg2==2.8.5