HHVM builds broken

[thekid]

See https://travis-ci.org/xp-framework/core/jobs/426839764:

Exception lang.Error (Class undefined: IllegalStateException)
  at <native>::Error(0, (0x26)'Class undefined: IllegalStateException')
  [line 132 of ConsoleTest.class.php]

The code here is:

try {
  Console::write(new class() implements Value {
    public function toString() { throw new IllegalStateException('Cannot render string'); }
    public function hashCode() { return get_class($this); }
    public function compareTo($value) { return 1; }
  });
  $this->fail('Expected exception not thrown', null, 'lang.IllegalStateException');
} catch (IllegalStateException $expected) {
  $this->assertEquals('', $this->streams[1]->getBytes());
}

Line 132 is the one with throw new IllegalStateException on it.

Problems caused by facebook/hhvm#8319

[thekid]

...which is why I allowed HHVM to fail for the moment in f9cd7be

commit f9cd7bebc00b9aacc29e9245acea529619e41fc8
Author: U-UNITED\friebe <[email protected]>
Date:   Thu Sep 6 21:38:27 2018 +0200

    Allow HHVM to fail

    *Sigh*: lang.Error (Class undefined: IllegalStateException)... what is this?
    See https://travis-ci.org/xp-framework/core/jobs/425404766