Async onInit doesn't catch promise rejection

[jcubic]

Issue summary

When you made an error in async onInit the error is not displayed on the terminal

Expected behavior

There should be an error on the terminal, so you can easily find it

Actual behavior

Errors are only in the Dev Tools console

Steps to reproduce

var term = $('body').terminal({}, {
  onInit: async function() {
       term.echo('Hello');
  }
});

This is a common error onInit is called before terminal returns, so you can't use term variable.