Allow osx builds to fail

.travis.yml

@@ -6,6 +6,7 @@ cache:
 
 # note: use py 3.5.2, it has lzma support. 3.5(.0) on travis.org/trusty does not.
 matrix:
+    fast_finish: true
     include:
         - python: 3.4
           os: linux
@@ -39,6 +40,8 @@ matrix:
           os: osx
           osx_image: xcode8.3
           env: TOXENV=py37
+    allow_failures:
+        - os: osx
 
 before_install:
 - |