remove usage of deprecated package github.com/coreos/go-etcd

[asilverman]

Currently viper is depending on a package that is deprecated, this issue is to request viper to upgrade its dependencies so it uses the maintained package found here https://github.com/etcd-io/etcd/tree/master/client

[sagikazarmark]

etcd is a transitive dependency, used by this package: https://github.com/bketelsen/crypt

Related bketelsen/crypt#6

[breml]

@sagikazarmark the issue in bketelsen/crypt#6 is fixed. I would really appreciate, if viper could be updated.

[breml]

Related: #956 and #957

[sagikazarmark]

The above PR will eventually solve this issue. It's currently blocked on etcd-io/etcd#12498 and etcd-io/etcd#12330