How to use the matchdep.filterPeer function in matchdep

grunt.registerTask('build', function () {
    var done = this.async();
    var when = require('when');
    var request = require('request');
    var _ = require('lodash');
    var deps = require('matchdep').filterPeer('grunt-contrib-*');
    var baseurl = 'http://raw.github.com/gruntjs/'

    // make http request for author file in a repo
    var authorFile = function (dep) {
      var deferred = when.defer();
      var url = baseurl+dep+'/master/AUTHORS';
      request.get({url: url}, function(err, res, body) {
        if (res.statusCode != 200) {
          grunt.fail.fatal('Failed to retrieve '+url);
        } else {
          deferred.resolve(body.split('\n'));
        }
      });
      return deferred.promise
    };

module.exports = function(grunt) {

  // Load all grunt-contrib peerDependencies.
  require('matchdep').filterPeer('grunt-contrib-*').forEach(grunt.loadNpmTasks);

};