tasks/datadriver.js
function() {
                var callback = arguments[arguments.length - 1];
                grunt.log.debug('init WebdriverIO instance');

                GLOBAL.browser.init(function(err) {
                    /**
                     * gracefully kill process if init fails
                     */
                    callback(err);
                });
            }
function() {
                var callback = arguments[arguments.length - 1];
                grunt.log.debug('init WebdriverIO instance');

                GLOBAL.browser.init(function(err) {
                    /**
                     * gracefully kill process if init fails
                     */
                    callback(err);
                });
            }
init WebdriverIO instance