code: func WithIgnoreFunc(fn func(err error, fields map[string]string) bool) OptionFunc {
  	return func(h *Hook) {
  		h.ignoreFunc = fn
  	}
  }
docs: // WithIgnoreFunc is an OptionFunc that receives the error and custom fields that are about
  // to be logged and returns true/false if it wants to fire a rollbar alert for.