Bump requests from 2.20.0 to 2.21.0 (#47)

Bumps [requests](https://github.com/requests/requests) from 2.20.0 to 2.21.0.
- [Release notes](https://github.com/requests/requests/releases)
- [Changelog](https://github.com/requests/requests/blob/master/HISTORY.md)
- [Commits](https://github.com/requests/requests/compare/v2.20.0...v2.21.0

)

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

requirements.txt

@@ -8,7 +8,7 @@ Pillow>=3.4.1
 protobuf==3.5.2.post1
 python-crfsuite==0.9.5
 Pyqtree==0.24
-requests==2.20.0
+requests==2.21.0
 sciencebeam-alignment==0.0.2
 sciencebeam-utils==0.0.1
 sklearn-crfsuite==0.3.6