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>

requirements.txt

@@ -5,7 +5,7 @@ django-easy-pdf==0.1.1
 djangorestframework==3.11.0
 gunicorn==19.7.1
 html5lib==1.0b10
-httplib2==0.18.0
+httplib2==0.19.0
 mysqlclient==1.3.12
 Pillow==7.1.0
 psycopg2==2.7.4