(node:6781) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 task_stop listeners added. Use emitter.setMaxListeners() to increase limit

1. Can't run on localhost on Mac OS for some reason.
2. Gulp stuck at max CPU

Here's my process:
1. [Install NodeJs](https://nodejs.org/en/)
2. `git clone https://github.com/ampproject/ampstart.git`
3. `cd ampstart`
4. `npm i`

Any help would be appreciated.

```
ampstart $ node -v
v9.2.0
ampstart $ npm run serve

> kickstart@ serve /Users/z/Documents/Work/GitHub/webdefrag/ampstart
> gulp serve

[16:38:35] Using gulpfile ~/Documents/Work/GitHub/webdefrag/ampstart/gulpfile.js
[16:38:35] Starting 'build:dev'...
[16:38:35] Starting 'escape'...
[16:38:36] Finished 'escape' after 167 ms
[16:38:36] Starting 'img'...
[16:38:40] Finished 'img' after 4.74 s
[16:38:40] Starting 'templateapi'...
[16:38:40] Finished 'templateapi' after 29 ms
[16:38:40] Starting 'postcss'...
[16:38:59] Finished 'postcss' after 19 s
[16:38:59] Starting 'posthtml'...
[16:39:00] Finished 'posthtml' after 1.26 s
[16:39:00] Starting 'www'...
[16:39:01] Finished 'www' after 680 ms
[16:39:01] Finished 'build:dev' after 26 s
[16:39:01] Starting 'watch:dev'...
[16:39:29] Finished 'watch:dev' after 28 s
[16:39:29] Starting 'serve'...
[16:39:29] Webserver started at http://localhost:8000
[16:39:29] Finished 'serve' after 12 ms
[16:39:30] Starting 'build:dev'...
[16:39:30] Starting 'escape'...
[16:39:33] Finished 'escape' after 2.88 s
[16:39:33] Starting 'img'...
[16:39:39] Finished 'img' after 5.9 s
[16:39:39] Starting 'templateapi'...
(node:6781) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 task_stop listeners added. Use emitter.setMaxListeners() to increase limit
(node:6781) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 task_err listeners added. Use emitter.setMaxListeners() to increase limit
```


Start by reproducing `npm run serve` on the reported Node.js version and read `gulpfile.js`, focusing on the `watch:dev`, `serve`, and repeated `build:dev` tasks. Confirm whether the listener warnings and high CPU reproduce, then document or verify a fix that allows the local server to run without the warning or runaway CPU usage.

Written by the indexing model from the issue text.