Bump httplib2 from 0.18.0 to 0.19.0 (#2150)

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)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -165,7 +165,7 @@ html5lib==1.1
     # via
     #   mitol-django-mail
     #   wagtail
-httplib2==0.18.0
+httplib2==0.19.0
     # via
     #   google-api-python-client
     #   google-auth-httplib2
@@ -258,6 +258,8 @@ pynacl==1.3.0
     # via -r requirements.in
 pyopenssl==17.5.0
     # via django-server-status
+pyparsing==2.4.7
+    # via httplib2
 python-dateutil==2.5.3
     # via
     #   botocore