Support PhantomJS 2.5

[Qazzian]

PhantomJS 2.5 is currently in beta and promises to support ES6.

There's already a ticket for phantomjs-prebuilt: Medium/phantomjs#668

Please can you update when it's possible so that we can update our test runners.

Thanks

[Arkni]

As soon as the linked ticket is resolved, we will see what we can do based on its outcomes

[anantha1995]

What version of phantomjs is it currently using?

[Arkni]

@anantha1995
Latest stable version: 2.1.1