Use macpython everywhere.

Add 3.6 for mac.

See zopefoundation/persistent#59

.travis.yml

@@ -16,15 +16,21 @@ matrix:
           python: pypy
         - os: linux
           python: pypy3
+        # It's important to use 'macpython' builds to get the least
+        # restrictive wheel tag. It's also important to avoid
+        # 'homebrew 3' because it floats instead of being a specific version.
         - os: osx
           language: generic
-          env: TERRYFY_PYTHON='homebrew 2'
+          env: TERRYFY_PYTHON='macpython 2.7'
         - os: osx
           language: generic
           env: TERRYFY_PYTHON='macpython 3.4'
         - os: osx
           language: generic
-          env: TERRYFY_PYTHON='homebrew 3'
+          env: TERRYFY_PYTHON='macpython 3.5'
+        - os: osx
+          language: generic
+          env: TERRYFY_PYTHON='macpython 3.6.0'
 before_install:
     - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then git clone https://github.com/MacPython/terryfy; fi
     - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then source terryfy/travis_tools.sh; fi