Update Travis setup

Author: jpadilla

.travis.yml

@@ -13,7 +13,11 @@ env:
   - DJANGO="django==1.4.13"
 
 install:
-  - pip install -r requirements.txt
+  - pip install $DJANGO
+  - pip install pytest-django==2.6.1
+  - pip install flake8==2.2.2
+  - "if [[ ${TRAVIS_PYTHON_VERSION::1} != '3' ]]; then pip install django-oauth2-provider==0.2.4; fi"
+  - export PYTHONPATH=.
 
 script:
   - ./runtests.py