Enable running on Mac

.travis.yml

@@ -10,6 +10,8 @@ addons:
     - libssl-dev
     - libunwind8
     - zlib1g
+before_install:
+  - if test "$TRAVIS_OS_NAME" == "osx"; then brew update; brew install icu4c; fi
 env:
   - KOREBUILD_DNU_RESTORE_CORECLR=true KOREBUILD_TEST_DNXCORE=true NO_PARALLEL_TEST_PROJECTS=E2ETests
 install:
@@ -22,5 +24,9 @@ install:
   - cd $OLDPWD
 mono:
   - 4.0.5
+os:
+  - linux
+  - osx
+osx_image: xcode7.1
 script:
   - ./build.sh --quiet verify