go-oidc using wrong import path

github.com/coreos/go-oidc has never used gopkg.in, and we may break this soon when we add a go.mod file (https://github.com/coreos/go-oidc/pull/228).

Just a heads up that you'll need to use the correct import path "github.com/coreos/go-oidc"

https://github.com/cloudflare/cloudflared/blob/7367827a1117932e0fbea37594b136ae4bf0ba33/validation/validation.go#L15