generate: exit when done and send back duration & errors

bin/nuxt-generate

@@ -24,6 +24,7 @@ var nuxt = module.exports = new Nuxt(options)
 nuxt.generate()
   .then(() => {
     console.log('[nuxt] Generate done') // eslint-disable-line no-console
+    process.exit(0)
   })
   .catch((err) => {
     console.error(err) // eslint-disable-line no-console

lib/generate.js

@@ -158,4 +158,5 @@ export default async function () {
     })
     console.error('==== Error report ==== \n' + report.join('\n\n')) // eslint-disable-line no-console
   }
+  return { duration, errors }
 }