change travis

Author: ejohnstown

.travis.yml

@@ -9,7 +9,7 @@ matrix:
       script:
         - ./make/manylinux1/build_wheels.sh
     - os: osx
-      osx_image: xcode9.4
+      osx_image: xcode8.3
       script:
         - ./make/osx/build_wheels.sh