Fix issue with undefined isProduction in Yarn scripts

[donker]

Resolves issue #5120

What it does is to replace the following:

module.exports = {

with

module.exports = (env, argv) => {
  const isProduction = argv.mode === "production";
  return {

for all the webpack configurations where we use isProduction. The command line p option (i.e. webpack -p) will now properly set isProduction in the configuration.

[valadas]

Looks good to me, nice catch there.

[david-poindexter]

Thank you so much @donker 🙏🏼