Move react{-dom,} to the common chunk in production too (#3690)
Move react{-dom,} to the common chunk in production too (#3690)

Without this, react-dom gets included in multiple pages.
flybayer/next.js,JeromeFitz/next.js,flybayer/next.js,BlancheXu/test,BlancheXu/test,JeromeFitz/next.js,azukaru/next.js,azukaru/next.js,flybayer/next.js,azukaru/next.js,JeromeFitz/next.js,zeit/next.js,flybayer/next.js,azukaru/next.js,zeit/next.js,zeit/next.js,JeromeFitz/next.js,BlancheXu/test