Apex domains cannot have CNAME records.
Question and response
Question
dig devs.futuro.pl. NS
Answer
devs.futuro.pl. 5 NS szafir.futuro.pl.
devs.futuro.pl. 5 NS dns2.futuro.pl.
devs.futuro.pl. 5 NS szmaragd.futuro.pl.
Authority
The response has no authority records.
Additional
dns2.futuro.pl. 5 A 87.204.28.12
szafir.futuro.pl. 5 A 62.233.128.17
szmaragd.futuro.pl. 5 A 62.233.128.18
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0