enable prod sourcemaps, closes #3626
closes #3626, Enable production sourcemaps.
@gl2748 could you please verify this is working in the dev environment?
This works on a local dev machine sourcemaps are visible in the browser console:
Similarly, running yarn run build shows sourcemaps are generated in the dist directory

However, when deploying the site as configured, to steemitdev.com, the sourcemaps are not visible.
Suspect it could be https://github.com/steemit/sdc-frontend config.
Test to see if it works via docker build, locally.
@roadscape tested on dev:
