HHVM build fails when instantiate `cli\Table` more than once

This PR is really bugreport to show that hhvm build fails.

I'm adding some acceptance tests for ASCII Tables and found that problem with hhvm.
Is hhvm really supported, planned to be supported or you can remove it from [travis config](https://github.com/wp-cli/php-cli-tools/blob/master/.travis.yml#L8) so I could include my tests in another PR?