Add Python 3 CI runners

.travis.yml

@@ -1,17 +1,31 @@
 matrix:
   include:
+    # Linux
     - sudo: required
       services:
         - docker
+      env:
+        - "PYTHON=python2"
+    - sudo: required
+      services:
+        - docker
+      env:
+        - "PYTHON=python3"
+    # macOS
     - os: osx
+      env:
+        - "PYTHON=python2"
+    - os: osx
+      env:
+        - "PYTHON=python3"
 
 script:
   - |
     if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
-      pip install .
-      python ./run_tests.py
+      $PYTHON -m pip install .
+      $PYTHON ./run_tests.py
     else
       # linux test requires root to clean up the wheelhouse (docker runs as root)
-      sudo pip install .
-      sudo python ./run_tests.py
+      sudo $PYTHON -m pip install .
+      sudo $PYTHON ./run_tests.py
     fi

appveyor.yml

@@ -1,5 +1,10 @@
+environment:
+  matrix:
+    - PYTHON: "C:\\Python27\\python.exe"
+    - PYTHON: "C:\\Python35\\python.exe"
+
 build_script:
-  - pip install .
+  - "%PYTHON% -m pip install ."
   # the '-u' flag is required so the output is in the correct order. 
   # See https://github.com/joerick/cibuildwheel/pull/24 for more info.
-  - python -u ./run_tests.py
+  - "%PYTHON% -u ./run_tests.py'