cd=false (DNSSEC) not respected in DNS over HTTPS JSON requests

The value of the `cd` (check disabled) flag was not correctly validated in DNS-over-HTTPS JSON API requests to cloudflare-dns.com. In result, despite explicitly setting the flag value to `0` or `false` (according to the [Cloudflare 1.1.1.1 documentation](https://developers.cloudflare.com/1.1.1.1/encryption/dns-over-https/make-api-requests/dns-json/)) the DNSSEC verification was not enforced for an unaware end user. The fix was released by Cloudflare Engineering team and the flag in question is now validated properly.