Request now understands HTTPS if variable is 'on' instead of 1

With HTTPS in Ubuntu/Apache superglobal `$_SERVER('HTTPS')` holds `'on'` instead of `1` and `Request::is('ssl')` was failing to understand that.

Inexplicably how, included tests against `'on'` and `'I am not empty'` values passed and still pass after this change but they don't work in reality.