build: correct minification (go back using UglifyJS 2)

Author: bbert

package.json

@@ -29,7 +29,7 @@
     "gulp-jshint": "2.0.4",
     "gulp-regexp-sourcemaps": "1.0.1",
     "gulp-sourcemaps": "2.6.1",
-    "gulp-uglify": "3.0.0",
+    "gulp-uglify": "2.1.2",
     "intern": "3.2.3",
     "jshint": "2.9.5",
     "jshint-stylish": "2.2.1",
@@ -38,4 +38,4 @@
     "yargs": "9.0.1",
     "browserstack-local": "latest"
   }
-}
+}