Mangle private properties when minifying

Private properties are indicated with a single
leading underscore.

Author: jamesls

Gruntfile.js

@@ -5,7 +5,8 @@ module.exports = function(grunt) {
     pkg: grunt.file.readJSON('package.json'),
     uglify: {
       options: {
-        banner: '/*! <%= pkg.name %> <%= grunt.template.today("yyyy-mm-dd") %> */\n'
+        banner: '/*! <%= pkg.name %> <%= grunt.template.today("yyyy-mm-dd") %> */\n',
+        mangleProperties: {regex: /^_/}
       },
       build: {
         src: '<%= pkg.name %>.js',