Unable to propagate error event from EventEmitter2

[agirorn]

Propagate could be enhanced to work with eventemmiter2 and not fail when the error event is emitted.
Relates to EventEmitter2/EventEmitter2#215

How to repoduce
``js
#!/usr/bin/env node

const EventEmitter2 = require('eventemitter2').EventEmitter2;
const propagate = require('propagate');

const source = new EventEmitter2();
const dest = new EventEmitter2();

propagate(source, dest);

dest.on('error', (error) => { console.log('got error event', error); });

console.log('sending error event');
try {
source.emit('error', 'The error data');
} catch(e) {
console.log('caught error', e);
}

```shell
sending error event
caught error Error: Uncaught, unspecified 'error' event.
    at EventEmitter.emit (/home/agirorn/tmp/test-propagate-eventemitter2/node_modules/eventemitter2/lib/eventemitter2.js:398:15)
    at EventEmitter.source.emit (/home/agirorn/tmp/test-propagate-eventemitter2/node_modules/propagate/index.js:19:13)
    at Object.<anonymous> (/home/agirorn/tmp/test-propagate-eventemitter2/test.js:15:10)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:383:7)
➜  test-propagate-eventemitter2

expected result

sending error event
got error event The error data

[pgte]

Gladly accepting code contributions :)

[DigitalBrainJS]

You should have at least one error listener in the source emitter to avoid throwing this error.
Since 6.1.0 we have the ignoreErrors option for the EventEmitter2 constructor to disable this behavior.