Introduce OS X CI testing

See https://docs.travis-ci.com/user/osx-ci-environment/ for more
information.

Author: ignisf

.travis.yml

@@ -4,12 +4,25 @@ rvm:
   - 2.1.8
   - 1.9.3
   - rbx
+matrix:
+  include:
+    - rvm: system
+      os: osx
+      osx_image: xcode7.3
+    - rvm: system
+      os: osx
+      osx_image: xcode6.4
+    - rvm: system
+      os: osx
+      osx_image: beta-xcode6.2
 bundler_args: --jobs=1 --retry=3
+before_install:
+  - if [ "$TRAVIS_OS_NAME" == "linux" ]; then sudo apt-get update; fi
+  - if [ "$TRAVIS_OS_NAME" == "linux" ]; then sudo apt-get install git-svn; fi
+  - if [ "$TRAVIS_OS_NAME" == "linux" ]; then gem update --system; fi
+  - if [ "$TRAVIS_OS_NAME" == "linux" ]; then gem update bundler; fi
+  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then sudo gem install bundler ; fi
 notifications:
   recipients:
     - cowboyd@thefrontside.net
     - bordjukov@gmail.com
-before_install:
-  - sudo apt-get update
-  - sudo apt-get install git-svn
-  - gem update bundler