grunt is not defined - AngularJs

This is my first test in grunt:). Anyway,I want to test my javasrcipt code using the different grunt modules. They are all installed and you can see them,in a json file called package.json.

{
   "name": "LarissaCity",
   "private": true,
   "devDependencies": {
     "grunt": "^1.0.1",
     "grunt-contrib-jshint": "^1.1.0",
     "jit-grunt": "^0.10.0",
     "jshint-stylish": "^2.2.1",
     "time-grunt": "^1.4.0"
  },
  "engines": {
  "node": ">=0.10.0"
  }
}

Next I have a file called Gruntfile.js. And inside it use the installed modules to test my javascript code. So.

'use strict';

 // Time how long tasks take. Can help when optimizing build times
 require('time-grunt')(grunt);

 // Automatically load required Grunt tasks
 require('jit-grunt')(grunt);

 // Define the configuration for all the tasks
 grunt.initConfig({
 pkg: grunt.file.readJSON('package.json'),

 // Make sure code styles are up to par and there are no obvious mistakes
jshint: {
options: {
  jshintrc: '.jshintrc',
  reporter: require('jshint-stylish')
},

all: {
  src: [
    'Gruntfile.js',
    'app/scripts/{,*/}*.js'
  ]
  }
 }
});

grunt.registerTask('build', [
'jshint'
]);

grunt.registerTask('default',['build']);

When I type grunt in the cmd this comes up.

 Loading "Gruntfile.js" tasks...ERROR
 ReferenceError: grunt is not defined

So maybe there is something wrong in the Gruntfile.js. Any ideas?

Thanks,

Theo.