Update babelrc and add sourcemap to production

[gauravtiwari]

• [Babel] Dynamic import() and Class Fields and Static Properties babel plugin to .babelrc
• Enable source-map in production

[swrobel]

I was just trying to figure out why sourcemaps are being generated in production and came across this, so at least I know it's intentional. What's the rationale behind enabling them in prod?

Edit: I see it's using nosources-source-map so the actual pre-Uglify source isn't included, just filenames & line numbers (I think). Here's the PR that made that change: #770

No need to respond at this point!