Add option to be able to specify a different path to publish from.

When it comes to publishing we want to publish the minified version that is built up in a different folder.  So to allow the option to specify a different root to publish from, I added the option for publishPath.
Thanks for the addition. Perhaps the following is an easier implementation of the function. Would this work for you?

    var options = config.getOptions();
    return run('npm', 'publish', options.publishPath || path || '.');