Fixed webpack config

server/webpack.config.js

@@ -5,7 +5,7 @@ const NodemonPlugin = require('nodemon-webpack-plugin')
 module.exports = env => {
 	const isProduction = !!env.production
 	const generateSourceMap = !!env.sourcemap
-	let devtool = null
+	let devtool = false
 	if (!isProduction) {
 		devtool = generateSourceMap ? 'source-map' : 'eval'
 	}