fix: add await to app.env.lookup() for async handling (#919)

Author: mshima

lib/routes/update.js

@@ -6,7 +6,7 @@ const successMessage = 'I\'ve just updated your generators. Remember, you can up
 
 async function updateSuccess(app) {
   console.log(`\n${chalk.cyan(successMessage)}\n`);
-  app.env.lookup();
+  await app.env.lookup();
   await app.updateAvailableGenerators();
   app.navigate('home');
 }