dev mode crashes poorly

[NfNitLoop]

Saw an issue today when running in dev mode:

• Saved a .ts file with invalid syntax.
• ESBuild failed to bundle the files.
• embedder.ts crashed.
• But the deno task serve which was serving the dev assets was still running, serving old assets.

This has two problems:

• Makes it hard to figure out why I'm not seeing my new code.
• Even on discovering that it's broken, now I have to find a dangling deno process to kill to clean up the old server.

Should make sure to kill the inner task process when the main task exits.

[NfNitLoop]

This might've been resolved already. Turns out I was using an older version.