Move uglifyjs-webpack-plugin to ^1.1.2

Fixes uglifyJs invalid assignment.
Before we were using the uglifyjs-webpack-plugin ^0.4.6 coming
from webpack.
Took from
https://github.com/webpack-contrib/uglifyjs-webpack-plugin/issues/187

Resolves openbmc/openbmc#3200

Change-Id: I29907caeeb49122cdddf6e6793070671a4525231
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/package.json b/package.json
index 6cbcc83..590f57f 100644
--- a/package.json
+++ b/package.json
@@ -101,6 +101,7 @@
     "rimraf": "^2.5.1",
     "run-sequence": "^1.1.2",
     "style-loader": "^0.19.0",
+    "uglifyjs-webpack-plugin": "^1.1.2",
     "webpack": "^3.6.0",
     "webpack-dev-server": "^2.9.1"
   },
diff --git a/webpack.config.js b/webpack.config.js
index dbdab02..be8e366 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -10,6 +10,7 @@
 var AssetsPlugin = require('assets-webpack-plugin');
 var CopyWebpackPlugin = require('copy-webpack-plugin');
 var path = require('path');
+var UglifyJsPlugin = require('uglifyjs-webpack-plugin')
 
 /**
  * Env
@@ -96,7 +97,7 @@
           // Transpile .js files using babel-loader
           // Compiles ES6 and ES7 into ES5 code
           test : /\.js$/,
-          loader : 'babel-loader',
+          use : 'babel-loader',
           exclude : /node_modules/
         },
         {
@@ -230,8 +231,10 @@
           // http://webpack.github.io/docs/list-of-plugins.html#uglifyjsplugin
           // Minify all javascript, switch loaders to minimizing mode
           // TODO: openbmc/openbmc#2781  Mangling currently breaks the GUI.
-          new webpack.optimize.UglifyJsPlugin({
-            mangle: false
+          new UglifyJsPlugin({
+            uglifyOptions:{
+              mangle: false
+            }
           }),
 
           // Copy assets from the public folder