[feature request] Emit source map for production bundle

[thangngoc89]

It would be great to have source map for production bundle. It should be behind a flag or something (shouldn't be the default behaviour )

I need this for uploading to Sentry.io (an error handling service).

I can send a PR to add this if you guys are up for it

[developit]

I think it's supposed to be enabled, but I guess it isn't being generated.