chore: changed webpack devtool to source-map to see the closest result to the sources.

webpack.dev.js

@@ -2,5 +2,5 @@ var merge = require('webpack-merge')
 var common = require('./webpack.common.js')
 
 module.exports = merge(common, {
-    devtool: process.env.DEBUG ? false : 'cheap-eval-source-map'
+    devtool: process.env.DEBUG ? false : 'source-map'
 })