1.x-dev currently triggers this:
Fatal error: Declaration of Drupal\\hcaptcha\\HCaptcha\\Drupal8Post::submit(string $url, array $params) must be compatible with Drupal\\hcaptcha\\HCaptcha\\RequestMethod::submit($url, array $params) in on line
This was introduced at some point after release 1.2.
Fixed
1.0
Code