Removed grunt-cli install script from Travis CI config file.
Removed grunt-cli install script from Travis CI config file.

Grunt version 1.0 was updated to support being run directly via npm
scripts. So there is no longer a need to have the grunt-cli package
installed globally before running `npm test`.

jasco/jquery-powertip,jasco/jquery-powertip,stevenbenner/jquery-powertip,stevenbenner/jquery-powertip