Bump djangorestframework from 3.6.2 to 3.9.1
Bump djangorestframework from 3.6.2 to 3.9.1

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.6.2 to 3.9.1.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](https://github.com/encode/django-rest-framework/compare/3.6.2...3.9.1)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
rkc007/Automated-Content-Grading-Using-Machine-Learning