Thow error if specified `ls` selector not found

lib/alias.js

@@ -9,6 +9,11 @@ export default class Alias extends Now {
   async ls (deployment) {
     if (deployment) {
       const target = await this.findDeployment(deployment);
+      if (!target) {
+        const err = new Error(`Aliases not found by "${deployment}". Run ${chalk.dim('`now alias ls`')} to see your aliases.`);
+        err.userError = true;
+        throw err;
+      }
 
       return this.retry(async (bail, attempt) => {
         const res = await this._fetch(`/now/deployments/${target.uid}/aliases`);