Add djangorestframework to Travis

Author: jpadilla

.travis.yml

@@ -16,6 +16,7 @@ install:
   - pip install $DJANGO
   - pip install pytest-django==2.6.1
   - pip install flake8==2.2.2
+  - pip install djangorestframework>=2.3.11
   - "if [[ ${TRAVIS_PYTHON_VERSION::1} != '3' ]]; then pip install django-oauth2-provider==0.2.4; fi"
   - export PYTHONPATH=.