chore: fix source map webpack build file

webpack.sourcemap.js

@@ -1,8 +1,7 @@
 var merge = require('webpack-merge')
-var common = require('./webpack.common.js')
+var production = require('./webpack.prod.js')
 
 // will create a build plus separate .min.js.map source map for debugging
-module.exports = merge(common, {
-    devtool: 'source-map',
-    mode: 'development'
+module.exports = merge(production, {
+    devtool: 'source-map'
 })