Trying to work around travis osx issues

.travis.yml

@@ -1,10 +1,11 @@
 language: python
-# python:
-#   - "2.7.15"
-#   - "3.6.6"
-#   - "3.7-dev"
+python:
+  - "2.7.15"
+  - "3.6.6"
+  - "3.7-dev"
 
 os: osx
+osx_image: xcode9.3
 
 git:
   depth: false