Build: Seasonal update of uglify and its options

raw     gz Compared to last run
 =      = dist/jquery.js
-294    -88 dist/jquery.min.js

Closes gh-3994

Gruntfile.js

@@ -259,9 +259,9 @@ module.exports = function( grunt ) {
 					banner: "/*! jQuery v<%= pkg.version %> | " +
 						"(c) JS Foundation and other contributors | jquery.org/license */",
 					compress: {
+						"pure_getters": true,
 						"hoist_funs": false,
 						loops: false,
-						unused: false,
 
 						// Support: IE <11
 						// typeofs transformation is unsafe for IE9-10

package.json

@@ -63,7 +63,7 @@
     "sizzle": "2.3.3",
     "strip-json-comments": "2.0.1",
     "testswarm": "1.1.0",
-    "uglify-js": "3.3.4"
+    "uglify-js": "3.3.12"
   },
   "scripts": {
     "build": "npm install && grunt",