Update dependency webpack-merge to v5

webpack/production.js

@@ -1,7 +1,7 @@
 // Note: You must restart bin/webpack-dev-server for changes to take effect
 console.log('Running in production mode'); // eslint-disable-line no-console
 
-const merge = require('webpack-merge');
+const { merge } = require('webpack-merge');
 const { BundleAnalyzerPlugin } = require('webpack-bundle-analyzer');
 const OfflinePlugin = require('offline-plugin');
 const UglifyJsPlugin = require('uglifyjs-webpack-plugin');