Firebase serve erroring on missing 404

[tettoffensive]

I'm trying to follow along with the youtube videos (https://www.youtube.com/watch?v=7IkUgCLr5oA&t=1s&list=PLl-K7zZEsYLkPZHe41m4jfAxUi0JjLgSM&index=3) and I have a simple cloud function which uses express. It runs fine when I deploy, but I would like to iterate on it locally.

Steps to reproduce

1. firebase serve --only functions --debug

[2019-02-27T23:28:50.511Z] Starting @google-cloud/functions-emulator
[2019-02-27T23:28:50.539Z] Parsing function triggers
Warning: You're using Node.js v11.10.0 but Google Cloud Functions only supports v6.11.5.
[2019-02-27T23:28:50.951Z] Error while deploying to emulator: Error: 404 page not found

Error: 404 page not found

    at new RequestError (/usr/local/lib/node_modules/firebase-tools/node_modules/googleapis/node_modules/google-auth-library/lib/transporters.js:34:42)
    at Request._callback (/usr/local/lib/node_modules/firebase-tools/node_modules/googleapis/node_modules/google-auth-library/lib/transporters.js:108:23)
    at Request.self.callback (/usr/local/lib/node_modules/firebase-tools/node_modules/request/request.js:185:22)
    at Request.emit (events.js:197:13)
    at Request.EventEmitter.emit (domain.js:446:20)
    at Request.<anonymous> (/usr/local/lib/node_modules/firebase-tools/node_modules/request/request.js:1161:10)
    at Request.emit (events.js:197:13)
    at Request.EventEmitter.emit (domain.js:446:20)
    at IncomingMessage.<anonymous> (/usr/local/lib/node_modules/firebase-tools/node_modules/request/request.js:1083:12)
    at Object.onceWrapper (events.js:285:13)
⚠  functions: Failed to emulate api
i  functions: No HTTPS functions found. Use firebase functions:shell if you would like to emulate other types of functions.

index.js:

'use strict';

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const express = require('express');
const app = express();

// GET /books
// Return all the recipe books
app.get('/books', async (request, response) => {
  admin.firestore().collection('books').get()
    .then(snapshot => {
      // Create array of books to return as json
      let books = []
      snapshot.forEach((childSnapshot) => {
        let item = childSnapshot.data()
        // Add the id of the object to the model
        item["id"] = childSnapshot.id;
        books.push(item);
      });
      response.send(books);
      return books;
    }).catch(error => {
      // Handle the error
      console.log(error);
      response.status(500).send(error);
    })
});

// Expose the API as a function
exports.api = functions.https.onRequest(app);

Environment details

• OS: macOS 10.14.2
• Node.js version: v11.10.0
• npm version: 6.8.0
• @google-cloud/functions-emulator version: not sure. using firebase 6.4.0