Enable Travis CI builds on Mac OS X.

Change-Id: I36a39720b34ccc58276f9943bf6ef289b1af9b1e
Reviewed-on: https://swiftshader-review.googlesource.com/11511
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/.travis.yml b/.travis.yml
index 92e428f..8ba6ac0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,8 +1,11 @@
 language: cpp
 
-os: linux
-dist: trusty
-sudo: false
+matrix:

+  include:

+    - os: linux

+      dist: trusty

+      sudo: false

+    - os: osx
 
 compiler:
   - clang