Merge pull request #530 from JrGoodle/travis-xctool-upgrade

Upgrade xctool on Travis instead of installing HEAD version

Author: pietbrauer

.travis.yml

@@ -1,9 +1,9 @@
 osx_image: xcode7
 language: objective-c
-before_install: brew update
-install:
-  - brew uninstall xctool && brew install --HEAD xctool
-  - script/bootstrap
+before_install:
+  - brew update
+  - brew outdated xctool || brew upgrade xctool
+install: script/bootstrap
 script: script/cibuild
 notifications:
   email: false