update to webpack 4

webpack/server.config.js

@@ -2,14 +2,16 @@ const config = require('sapper/webpack/config.js');
 const webpack = require('webpack');
 const ExtractTextPlugin = require("extract-text-webpack-plugin");
 const UglifyJSPlugin = require('uglifyjs-webpack-plugin');
+const pkg = require('../package.json');
 
 module.exports = {
 	entry: config.server.entry(),
 	output: config.server.output(),
 	target: 'node',
 	resolve: {
-		extensions: ['.js', '.html', '.json']
+		extensions: ['.js', '.json', '.html']
 	},
+	externals: Object.keys(pkg.dependencies),
 	module: {
 		rules: [
 			{
@@ -26,5 +28,9 @@ module.exports = {
 				}
 			}
 		]
+	},
+	mode: process.env.NODE_ENV,
+	performance: {
+		hints: false // it doesn't matter if server.js is large
 	}
 };