Use google.golang.org/grpc v1.29.1 to fix a dependency issue

go.etcd.io/etcd depends on deprecated packages of gRPC that have
been removed. This causes that go mod cannot build the dependency
tree and utilities like `go mod tidy` or `go mod vendor` does not
work properly.

This fix uses a gRPC version that supports old and new interfaces.
So it can be used by etcd and google cloud packages.

Fixes #377

go.mod

@@ -10,9 +10,7 @@ require (
 	github.com/corpix/uarand v0.1.1 // indirect
 	github.com/google/uuid v1.1.2
 	github.com/icrowley/fake v0.0.0-20180203215853-4178557ae428
-	github.com/juju/ansiterm v0.0.0-20180109212912-720a0952cc2a // indirect
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51 // indirect
-	github.com/lunixbochs/vtclean v1.0.0 // indirect
 	github.com/manifoldco/promptui v0.8.0
 	github.com/pkg/errors v0.9.1
 	github.com/pquerna/otp v1.0.0
@@ -30,11 +28,18 @@ require (
 	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897
 	golang.org/x/net v0.0.0-20201021035429-f5854403a974
 	golang.org/x/sys v0.0.0-20201022201747-fb209a7c41cd
-	google.golang.org/grpc/examples v0.0.0-20201013205100-7745e521ff61 // indirect
 	gopkg.in/square/go-jose.v2 v2.5.1
 	software.sslmate.com/src/go-pkcs12 v0.0.0-20201103104416-57fc603b7f52
 )
 
+// This is a temporal workaround to fix a dependency problem between etcd and
+// gRPC. The gRPC v1.29.1 supports old a new interfaces, so it can be used by
+// packages using the old (go.etcd.io/etcd) and new (cloud.google.com)
+// interfaces.
+//
+// For more information see https://github.com/etcd-io/etcd/issues/12124
+replace google.golang.org/grpc => google.golang.org/grpc v1.29.1
+
 // replace github.com/smallstep/certificates => ../certificates
 // replace github.com/smallstep/certinfo => ../certinfo
 // replace go.step.sm/crypto => ../crypto