don't install ujson, it's broken on pypy

.travis.yml

@@ -9,7 +9,6 @@ before_script:
   - curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
   - chmod +x ./cc-test-reporter
   - ./cc-test-reporter before-build
-  - pip install --upgrade setuptools pip
   - pip install -r requirements.txt
   - pip install -U pytest-xdist pytest-cov pytest pytest-forked pluggy py
   - python setup.py install

requirements.txt

@@ -2,4 +2,3 @@ psutil
 pyyaml
 toml
 requests
-ujson