the dev server crashes when we remove or rename a file

[Fil]

to reproduce:

cd cli/
yarn dev

open http://127.0.0.1:3000/markdown

mv docs/markdown.md ./

navigate to http://127.0.0.1:3000/javascript by clicking on "JavaScript reference" in the side bar

↑ {
  type: 'hello',
  path: '/markdown',
  hash: '13f37e067d6239136c9165ffd158da4161de47b99b8c55d7441d387ffd4b1e04'
}
node:internal/process/promises:289
            triggerUncaughtException(err, true /* fromPromise */);
            ^

[Error: ENOENT: no such file or directory, open 'docs/markdown.md'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: 'docs/markdown.md'
}

[wiltsecarpenter]

This is now fixed in main, but I was unsure what to do when a markdown file is deleted or renamed. For now, it just ignores that event, which means the client will stop receiving updates, but will continue to show whatever it last had.