fix: Depend on PhantomJS 1.9 to fix path issue and be at latest stable.

I was having issues with require('phantomjs').path not pointing to correctly place and finally found a ton of other people having same issue. 

PhantomJS 1.9 dependency fixes this issue. 1.9 has been out a while and fixes some other legit bugs in 1.8 so it'll be good to upgrade.

References: 
- gruntjs/grunt-lib-phantomjs#17.
- https://groups.google.com/forum/#!searchin/karma-users/phantomjs/karma-users/20l4wI1YUnA/jgTZkektpvQJ