How to run grunt docular-server?

if I execute the command grunt docular-server

I get the error message:

ERROR: Could not start node server [TypeError: Object #<Object> has no method 'server']

then the docular-server is not running.

I installed grunt to make a documentation of my code like this:

 `npm install -g grunt-cli`
 `npm install grunt grunt-docular`

My Gruntfile.js looks like this:

module.exports = function(grunt) {

// Project configuration.
grunt.initConfig({

pkg: grunt.file.readJSON('package.json'),

docular: {
groups: [],
showDocularDocs: true,
showAngularDocs: true
}

});

// Load the plugin that provides the "docular" tasks.
grunt.loadNpmTasks('grunt-docular');

// Default task(s).
grunt.registerTask('default', ['docular']);

};

this example is taken from the official site here:

http://grunt-docular.com/documentation/docular/docularinstall/installdocular