build(deps): Bump github.com/golang/protobuf from 1.4.3 to 1.5.1

Bumps [github.com/golang/protobuf](https://github.com/golang/protobuf) from 1.4.3 to 1.5.1.
- [Release notes](https://github.com/golang/protobuf/releases)
- [Commits](golang/protobuf@v1.4.3...v1.5.1)

Signed-off-by: dependabot[bot] <support@github.com>

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/confio/ics23/go v0.6.3
 	github.com/gogo/gateway v1.1.0
 	github.com/gogo/protobuf v1.3.2
-	github.com/golang/protobuf v1.4.3
+	github.com/golang/protobuf v1.5.1
 	github.com/grpc-ecosystem/go-grpc-middleware v1.2.2
 	github.com/grpc-ecosystem/grpc-gateway v1.16.0
 	github.com/pkg/errors v0.9.1