fix: relay IntercomAPI secondary arguments (2.0)

[nikparo]

Currently the secondary arguments of IntercomAPI in 2.0 get passed through as an array, meaning that e.g. onShow and onHide won't work. I.e.

window.Intercom.apply(null, [method, args]);

Should be:

window.Intercom.apply(null, [method, ...args]);

However, with the above fix npm run build throws an error:

Error: '__spreadArrays' is not exported by tslib

This may be solvable by updating the correct packages. Alternatively, the code can be written as it is in this pull request or something like:

export default function(method: string, ...args: Array<any>) {
  if (window.Intercom) {
    args.unshift(method);
    window.Intercom.apply(null, args);
  } else {
    console.warn('Intercom not initialized yet');
  }
}