PhantomJS driver does not launch on Windows

When not using a system path for PhantomJS, the process env. path is
appended to include the PhantomJS directory from the node dependencies.
However, this path concatenation uses colon, which works on *nix and mac
machines, but not on Windows. Windows requires path concatenation with
semi-colon.
Fail grunt when tests fail

Fast fail grunt when tests fail.
Merge pull request #27 from atifsyedali/master

PhantomJS driver does not launch on Windows