ci: Update Travis-CI to use Ubuntu Linux 14.04 (trusty) and OS X 10.9 VMs

Travis-CI has the following build matrix:
- Ubuntu Linux 14.04, gcc 4.8.4
- Ubuntu Linux 14.04, clang 3.5.0
- OS X 10.9, clang 600.0.57 (based on LLVM 3.5svn)

Change-Id: I37f345f0dcd2b3712b2bd2db5f5cb87ddd7a628f
Refs: #3360
diff --git a/.travis.yml b/.travis.yml
index 7f40779..9503148 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,15 +1,21 @@
-sudo: true
-language: cpp
-os:
-  - linux
-compiler:
-  - gcc
+sudo: required
+language: generic
+matrix:
+  include:
+    - os: linux
+      dist: trusty
+      compiler: gcc
+    - os: linux
+      dist: trusty
+      compiler: clang
+    - os: osx
+      compiler: clang
 notifications:
   email:
     on_success: always
     on_failure: always
 script:
-  - if [[ $TRAVIS_OS_NAME == linux ]]; then export NODE_LABELS="Linux Ubuntu Ubuntu-12.04"; fi
-  - if [[ $TRAVIS_OS_NAME == osx ]]; then export NODE_LABELS="OSX OSX-10.10"; fi
+  - if [[ $TRAVIS_OS_NAME == linux ]]; then export NODE_LABELS="Linux Ubuntu Ubuntu-14.04"; fi
+  - if [[ $TRAVIS_OS_NAME == osx ]]; then export NODE_LABELS="OSX OSX-10.9"; fi
   - echo $NODE_LABELS
   - ./.jenkins