Apex domains cannot have CNAME records.
Question and response
Question
dig gasigma.org. NS
Answer
gasigma.org. 5 NS ns-42.awsdns-05.com.
gasigma.org. 5 NS ns-1340.awsdns-39.org.
gasigma.org. 5 NS ns-1187.awsdns-20.org.
gasigma.org. 5 NS ns-407.awsdns-50.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0