v0.6.1-2 image does not work anymore

Recent notary `v0.6.1-2` image does not work any more, because the binary was built with golang `1.15` and hit the issue https://github.com/dvsekhvalnov/jose2go/issues/26 . The current Dockerfile does not specify golang version and golang version might have changed in `alpine:3.13` .

Other related issue: https://github.com/notaryproject/notary/issues/1602 