Use Xcode 9.4 for travis.

Luc Dion · Luc Dion · commit 04e463e230e7 · 2018-06-28T09:29:54.000-04:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 language: objective-c
-osx_image: xcode9.2 
+osx_image: xcode9.4 
 
 before_install:
   - gem install xcpretty-travis-formatter;
