Update to the new Travis CI infrastructure.

http://docs.travis-ci.com/user/migrating-from-legacy/#Why-migrate-to-container-based-infrastructure%3F

.travis.yml

 language: node_js
 
-env: SKIP_SASS_BINARY_DOWNLOAD_FOR_CI=true
+env: SKIP_SASS_BINARY_DOWNLOAD_FOR_CI=true CC=gcc-4.7 CXX=g++-4.7 LINK=gcc-4.7 LINKXX=g++-4.7
 
 compiler: gcc
 
+sudo: false
+
 node_js:
   - "0.10"
   - "0.12"
@@ -15,14 +17,16 @@ node_js:
 matrix:
   fast_finish: true
 
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - gcc-4.7
+      - g++-4.7
+
 before_install:
-  - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
-  - sudo apt-get update
-  - sudo apt-get install gcc-4.7 g++-4.7
-  - sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.7 20
-  - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.7 20
   - g++ --version
-  - sudo apt-get update -qq
   - git submodule update --init --recursive
 
 after_success: npm run-script coverage