load-grunt-tasks For Gruntfile.js

Reduce duplication of list of grunt tasks. Previously, the same list existed in both
package.json and Gruntfile.js. Code and author for load-grunt-tasks.js:

http://travis-ci.org/sindresorhus/load-grunt-tasks

As per the author's readme.md, replace in Gruntfile.js, in this instance:

grunt.loadNpmTasks('grunt-contrib-uglify');
grunt.loadNpmTasks('grunt-contrib-cssmin');
grunt.loadNpmTasks('grunt-contrib-jshint');
grunt.loadNpmTasks('grunt-contrib-concat');
grunt.loadNpmTasks('grunt-contrib-clean');
grunt.loadNpmTasks('grunt-contrib-copy');
grunt.loadNpmTasks('grunt-chmod');
grunt.loadNpmTasks('grunt-contrib-watch');

with:

require('load-grunt-tasks')(grunt);

At which point, bob's your uncle and the grunt command works as expected.