Use mirror to download PhantomJS

BitBucket download is really unreliable and fails our Ruby builds

Author: p0deje

.travis.yml

@@ -47,7 +47,7 @@ script:
   - |
     if [[ $RB_FILES_CHANGED == rb/* ]]; then
       export PHANTOMJS_NAME=phantomjs-2.1.1-linux-x86_64
-      curl -L -O "https://bitbucket.org/ariya/phantomjs/downloads/${PHANTOMJS_NAME}.tar.bz2"
+      curl -L -O "https://cnpmjs.org/mirrors/phantomjs/${PHANTOMJS_NAME}.tar.bz2"
       tar -xvjf $PHANTOMJS_NAME.tar.bz2
       chmod +x $PHANTOMJS_NAME/bin/phantomjs
       mv $PHANTOMJS_NAME/bin/phantomjs chrome-linux/phantomjs