Update xcode version to 7.3 in travis config

SebastianOsinski · SebastianOsinski · commit ddf653b8d02b · 2016-03-19T17:49:31.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -6,4 +6,4 @@ before_install:
   - gem install xcpretty --no-document
 script:
   - make test
-osx_image: xcode7
+osx_image: xcode7.3
