Install phantomjs with npm

.travis.yml

@@ -2,8 +2,7 @@ language: ruby
 sudo: false
 cache:
   - bundler
-  - directories:
-    - travis-phantomjs
+  - $(npm bin -g)/phantomjs
 bundler_args: --without development
 rvm:
   - "2.1.5"
@@ -30,10 +29,9 @@ before_script:
   - cp config/application.yml.example config/application.yml
   - RAILS_ENV=test bundle exec rake db:create db:schema:load
 
-  - mkdir -p travis-phantomjs
-  - wget -nc https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-2.1.1-linux-x86_64.tar.bz2 -O $PWD/travis-phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2 || true
-  - tar -xvf $PWD/travis-phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2 -C $PWD/travis-phantomjs
-  - export PATH=$PWD/travis-phantomjs/phantomjs-2.1.1-linux-x86_64/bin:$PATH
+  # Only install PhantomJS if it is not already present (ie. cached)
+  - npm list -g phantomjs-prebuilt@~2.1.7 --depth=0 || npm install -g phantomjs-prebuilt@~2.1.7
+  - export PATH=`npm bin -g`:$PATH
 
   - >
     if [ "$KARMA" = "true" ]; then