use phantomjs 2.1.1 (instead of 1.9.8 which is travis default)

per: travis-ci/travis-ci#3225 (comment)

Author: dylanfprice

.travis.yml

@@ -2,6 +2,20 @@ language: node_js
 node_js:
   - "0.10"
 
+cache:
+  directories:
+    - "travis_phantomjs"
+
+before_install:
+  - export PHANTOMJS_VERSION=2.1.1
+  - phantomjs --version
+  - export PATH=$PWD/travis_phantomjs/phantomjs-$PHANTOMJS_VERSION-linux-x86_64/bin:$PATH
+  - phantomjs --version
+  - if [ $(phantomjs --version) != $PHANTOMJS_VERSION ]; then rm -rf $PWD/travis_phantomjs; mkdir -p $PWD/travis_phantomjs; fi
+  - if [ $(phantomjs --version) != $PHANTOMJS_VERSION ]; then wget https://github.com/Medium/phantomjs/releases/download/v$PHANTOMJS_VERSION/phantomjs-$PHANTOMJS_VERSION-linux-x86_64.tar.bz2 -O $PWD/travis_phantomjs/phantomjs-$PHANTOMJS_VERSION-linux-x86_64.tar.bz2; fi
+  - if [ $(phantomjs --version) != $PHANTOMJS_VERSION ]; then tar -xvf $PWD/travis_phantomjs/phantomjs-$PHANTOMJS_VERSION-linux-x86_64.tar.bz2 -C $PWD/travis_phantomjs; fi
+  - phantomjs --version
+
 before_script:
   - export DISPLAY=:99.0
   - export PHANTOMJS_BIN=/usr/local/phantomjs/bin/phantomjs