Merge pull request #377 from KineticTheory/fix_travis

WIP: Try to fix pip upgrade failure in Travis.

.travis.yml

@@ -40,7 +40,7 @@ addons:
 
 before_install:
   - mkdir -p ${VENDOR_DIR}/bin & export PATH=${VENDOR_DIR}/bin:$PATH
-  - pip install --upgrade pip
+  - pip install --upgrade --user pip
 #  - pip install --upgrade setuptools
   - if [[ ${COVERAGE}  ]]; then pip install --user codecov; fi