add grunt-contrib-jshint

step5-Gruntfile.js

module.exports = function(grunt) {
  grunt.loadNpmTasks('grunt-contrib-jshint');

  grunt.initConfig({
    jshint: {
      all: ['js/app/**/*.js'],
      options : {
        esnext : true
      }
    }
  });
  
  grunt.task.registerTask('local', ['jshint', 'emberhandlebars', 'transpile:app', 'concat:dist']);
}