Move `eslint` package to `peerDependencies`

[ljharb]

It'd be great if you added eslint to peerDependencies, so that npm can programmatically ensure i have a compatible eslint.

[phanect]

That sounds reasonable.
When I made this plugin, I added eslint to dependencies because it calls its API, but peerDependencies should be the better option.

[ljharb]

You can add it to both, too.