Travis: Simplify now that 14.04 is available

.travis.yml

@@ -3,18 +3,12 @@ compiler:
   - clang
   - gcc
 
-before_install:
-  # Ubuntu 12.04 doesn't have carton natively, so we install the copy from trusty
-  # This can be removed when Travis CI updates to 14.04
-  # https://github.com/travis-ci/travis-ci/issues/2046
-  - lsb_release -r
-  - sudo apt-add-repository 'deb http://archive.ubuntu.com/ubuntu trusty main universe multiverse'
-  - sudo apt-get update
-
-  # Ubuntu's versions of these packages are out of date so we need
-  # to install them using carton instead.
-  - sudo apt-get --no-install-recommends install carton
+addons:
+    apt:
+        packages:
+            - carton
 
+before_install:
   # Fetch nginx source
   - wget http://nginx.org/download/nginx-${NGINX_VERSION}.tar.gz
   - tar xvfz nginx-${NGINX_VERSION}.tar.gz