Change to ESM only #193

Hello,

Currently wait-on package ships with commonjs but requires node 20, since node 20 is possible for a ESM package to be imported with require https://nodejs.org/en/blog/release/v23.0.0#requireesm-is-now-enabled-by-default could we change the lib to ship with ESM instead of CJS ? Is this planned ? Since 20.19.0 it doesn't even require a flag anymore

Thanks.