Build attempt on Fedora 33 failed

[marbu]

I tried to build ceph nano on Fedora 33 with golang-1.15.11-1.fc33.x86_64 and run into this error:

$ make
rm -f cn cn &>/dev/null || true
dep ensure
unset GOOS; unset GOARCH; cd cmd; go test -timeout 1m -count 5
# github.com/ceph/cn/cmd
./start.go:198:49: conversion from int64 to string yields a string of one rune, not a string of digits (did you mean fmt.Sprint(x)?)
FAIL	github.com/ceph/cn/cmd [build failed]
make: *** [Makefile:29: prepare] Error 2