fix(cli): Windows - deno install shim should use first Deno executable on PATH rather than explictly deno.exe

[dsherret]

Right now, deno install produces a shim like the following:

% generated by deno install %
@deno.exe "run" "--allow-read" "--allow-write" "--allow-net" "--allow-env" "--allow-run" "--no-check" "https://deno.land/x/deploy/deployctl.ts" %*

This is incorrect because the deno command might not be deno.exe (as is the case on my system where it runs from deno.cmd or deno.ps1 via bvm).

This fix does the following:

1. It uses the first deno executable on the PATH, so it works the same way as executing the deno command.
2. It supports more than just a deno.exe executable being on the path.

[lucacasonato]

LGTM. Thanks