Make it more spec compliant

When used with mocha the errors are displayed twice. Is there a way to have it only display once?

const AggregateError = require('aggregate-error')

it('should fail', function() {
  throw new AggregateError([
    new Error('first'),
    new Error('second')
  ])
})

The report is

  1) should fail

  0 passing (12ms)
  1 failing

  1) should fail:
     
    Error: first
        at Context.<anonymous> (/Users/williamrusnack/Documents/event_sequencing/try_aggregate-error.js:5:5)
        at callFn (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runnable.js:354:21)
        at Test.Runnable.run (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runnable.js:346:7)
        at Runner.runTest (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:442:10)
        at /Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:560:12
        at next (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:356:14)
        at /Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:366:7
        at next (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:290:14)
        at Immediate.<anonymous> (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:334:5)
    Error: second
        at Context.<anonymous> (/Users/williamrusnack/Documents/event_sequencing/try_aggregate-error.js:6:5)
        at callFn (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runnable.js:354:21)
        at Test.Runnable.run (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runnable.js:346:7)
        at Runner.runTest (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:442:10)
        at /Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:560:12
        at next (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:356:14)
        at /Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:366:7
        at next (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:290:14)
        at Immediate.<anonymous> (/Users/williamrusnack/Documents/event_sequencing/node_modules/mocha/lib/runner.js:334:5)
  AggregateError: 
      Error: first
          at Context.<anonymous> (try_aggregate-error.js:5:5)
      Error: second
          at Context.<anonymous> (try_aggregate-error.js:6:5)
      at Context.<anonymous> (try_aggregate-error.js:4:9)

Reproduce the shown AggregateError output with the provided Mocha test and inspect the package's error-formatting entry point. Determine why the individual errors and aggregate error are both rendered, then add or update coverage for the reproduction so the output contains each error only once.