Bump httplib2 from 0.9.2 to 0.18.0

Bumps [httplib2](https://github.com/httplib2/httplib2) from 0.9.2 to 0.18.0.
- [Release notes](https://github.com/httplib2/httplib2/releases)
- [Changelog](https://github.com/httplib2/httplib2/blob/master/CHANGELOG)
- [Commits](httplib2/httplib2@0.9.2...v0.18.0)

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

Author: dependabot[bot]

requirements.txt

@@ -35,7 +35,7 @@ Flask-Cors==3.0.8
 Flask-Ext==0.1
 Flask-RESTful==0.3.7
 gensim==3.8.3
-httplib2==0.9.2
+httplib2==0.18.0
 idna==2.8
 idna-ssl==1.1.0
 ipykernel==5.1.2