Support `deps.ts` (or drop replacement for `import_map.json`)

Hi,

I thought `import_map.json` is the old way of Deno to manage dependencies, now it's [deps.ts](https://docs.deno.com/runtime/tutorials/manage_dependencies)/`dev_deps.ts` (with `-D` flag) if I'm not wrong about that... I feel like it's the natural way of managing dependencies, so deno can cooperate with `trex` to make things easier.
