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

@@ -3,7 +3,7 @@ audioread==2.1.5
 Cython==0.26.1
 decorator==4.1.2
 google-api-python-client==1.6.3
-httplib2==0.18.0
+httplib2==0.19.0
 joblib==0.11
 librosa==0.5.1
 numpy==1.13.1