Workaround for PhantomJS 1.9.8

Hi,

PhantomJS 1.9.8 logs some warning messages to STDOUT and that causes failures when parsing JSON response. Please see https://github.com/ariya/phantomjs/issues/12697 for details. The only workaround that seems to work is to stick `phantom.exit` inside a `setTimeout` call.
As this is a workaround I'm not sure you'll want to merge this, but as far as I know it's impossible to run `guard-jasmine` with PhantomJS 1.9.8 and, from what I see on that issue, they won't be releasing a fix for that in 1.9.x series.