Fix @babel/env modules config (#5119)
Fix @babel/env modules config (#5119)

Probably an oversight but currently env preset's `modules` option always evaluates to 'auto'. We probably want it to be set to false, especially in prod, to have Webpack handle modules natively.
JeromeFitz/next.js,azukaru/next.js,BlancheXu/test,BlancheXu/test,flybayer/next.js,flybayer/next.js,flybayer/next.js,JeromeFitz/next.js,JeromeFitz/next.js,azukaru/next.js,flybayer/next.js,azukaru/next.js,zeit/next.js,BlancheXu/test,zeit/next.js,zeit/next.js,azukaru/next.js,JeromeFitz/next.js