Cannot visualize crawl.json in D3

I use Node v10.13.0. I checked out the puppeteer examples repo, ran `yarn install`, ran `crawlsite.js`, got a good `crawl.json` in the output, but when I run `node server.js` to try to visualize in D3, I . just get a `Cannot GET` message in the browser. There is no console output from `server.js` in the terminal. Any ideas?