Update to be grunt 0.4.x compatible

[JamesMGreene]

When I try to utilize the htmllint task with grunt 0.4.0a, it fails:

Running "htmllint:all" (htmllint) task
Warning: Cannot call method 'spawn' of undefined Use --force to continue.

Aborted due to warnings.

Here's my [simplified] "Gruntfile.js" configuration:

module.exports = function(grunt) {
  grunt.initConfig({
    htmllint: {
      all: ['*.html']
    }
  });

  grunt.loadNpmTasks('grunt-html');

  grunt.registerTask('default', ['htmllint']);
};

[JamesMGreene]

This seems to be directly related to Issue #3.

[jzaefferer]

Was fixed with the 0.3.x release.