build error on master branch

[tomek-US]

$ git chackout master
Switched to branch 'master'
Your branch is up to date with 'origin/master'.

$ make all
[...]
google.golang.org/protobuf/types/descriptorpb
# github.com/openconfig/ygot/proto/yext
build/gopkgs/src/github.com/openconfig/ygot/proto/yext/yext.pb.go:44:11: undefined: "github.com/golang/protobuf/proto".ProtoPackageIsVersion4
# github.com/openconfig/ygot/proto/ywrapper
build/gopkgs/src/github.com/openconfig/ygot/proto/ywrapper/ywrapper.pb.go:46:11: undefined: "github.com/golang/protobuf/proto".ProtoPackageIsVersion4
# github.com/openconfig/gnmi/proto/gnmi_ext
build/gopkgs/src/github.com/openconfig/gnmi/proto/gnmi_ext/gnmi_ext.pb.go:47:11: undefined: "github.com/golang/protobuf/proto".ProtoPackageIsVersion4
make: *** [/go/src/app/build/gopkgs/.done] Error 2
Makefile:73: recipe for target '/go/src/app/build/gopkgs/.done' failed
$