Apex domains cannot have CNAME records.
Question and response
Question
dig ci-servers.org. NS
Answer
ci-servers.org. 5 NS nsa.dnsnode.net.
ci-servers.org. 5 NS nsp.dnsnode.net.
ci-servers.org. 5 NS nsu.dnsnode.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0