Enable ES6 support by using babelify transform in browserify build

* Add babelify as dev dependency
* Add babelify transform to browserify build
* Enable es6 support for jshint
* Ignore minified js files in babel transform

.jshintrc

@@ -16,6 +16,7 @@
 	"trailing": true,
 	"undef": true,
 	"unused": true,
+	"esnext": true,
 
 	"predef": [
 			"console",

Gruntfile.js

@@ -18,7 +18,13 @@ module.exports = function(grunt) {
           browserifyOptions: {
             standalone: 'openpgp'
           },
-          external: [ 'crypto', 'node-localstorage' ]
+          external: [ 'crypto', 'node-localstorage' ],
+          transform: [
+            ["babelify", {
+              ignore: ['*.min.js'],
+              presets: ["es2015"]
+            }]
+          ]
         }
       },
       openpgp_debug: {
@@ -30,7 +36,13 @@ module.exports = function(grunt) {
             debug: true,
             standalone: 'openpgp'
           },
-          external: [ 'crypto', 'node-localstorage' ]
+          external: [ 'crypto', 'node-localstorage' ],
+          transform: [
+            ["babelify", {
+              ignore: ['*.min.js'],
+              presets: ["es2015"]
+            }]
+          ]
         }
       },
       worker: {

package.json

@@ -32,6 +32,8 @@
     "test": "grunt test"
   },
   "devDependencies": {
+    "babel-preset-es2015": "^6.3.13",
+    "babelify": "^7.2.0",
     "chai": "~3.4.1",
     "coveralls": "^2.11.2",
     "grunt": "~0.4.5",