Update pip as per pypa/setuptools#951

Author: kevinkjt2000

.travis.yml

@@ -6,6 +6,7 @@ python:
   - 3.7
   - 2.7
 install:
+  - pip install --upgrade pip
   - if [[ $TRAVIS_PYTHON_VERSION == 2* ]]; then pip install -r requirements/python2.txt; fi
   - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then pip install -r requirements/python3.txt; fi
 script: nosetests