There’s an issue for this in Launchpad: https://bugs.launchpad.net/snapcraft/+bug/1802256
I ran into the same issue as @eberkund too.
Pulling fluxctl
go get -t -d ./github.com/weaveworks/flux/...
go get: -t flag is a no-op when using modules
go: cannot find main module; see 'go help modules'
Failed to run 'go get -t -d ./github.com/weaveworks/flux/...' for 'fluxctl': Exited with code 1.