Update Next.js docs with NODE_ENV=production

I just realised I’ve had a next.js app running without NODE_ENV=production for a while, if I fucked this up I bet others did too.

This needs updating: Deploy a Next.js App | Render · Cloud Hosting for Developers

Environment: NODE_ENV=production
Build command: yarn --frozen-lockfile --prod=false && yarn build

Hi @KATT ,

Thanks for letting us know! I’ve pushed a change to set NODE_ENV in the render.yaml.