update google.golang.org/grpc to version 1.38.0

In version 1.38.0 the interface of ClientConns changed.
UpdateState() now returns an error.
The interface is used only in the testcases, adapt it to the new interface.

Author: Fabian Holler

go.mod

@@ -2,6 +2,10 @@ module github.com/simplesurance/grpcconsulresolver
 
 require (
 	github.com/armon/go-metrics v0.0.0-20190430140413-ec5e00d3c878 // indirect
+	github.com/cespare/xxhash/v2 v2.1.1 // indirect
+	github.com/cncf/udpa/go v0.0.0-20210930031921-04548b0d99d4 // indirect
+	github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1 // indirect
+	github.com/envoyproxy/go-control-plane v0.9.10-0.20210907150352-cf90f659a021 // indirect
 	github.com/hashicorp/consul/api v1.2.0
 	github.com/hashicorp/go-immutable-radix v1.1.0 // indirect
 	github.com/hashicorp/go-msgpack v0.5.5 // indirect
@@ -10,10 +14,7 @@ require (
 	github.com/hashicorp/memberlist v0.1.5 // indirect
 	github.com/hashicorp/serf v0.8.5 // indirect
 	github.com/miekg/dns v1.1.2 // indirect
-	golang.org/x/crypto v0.0.0-20190701094942-4def268fd1a4 // indirect
-	golang.org/x/net v0.0.0-20190503192946-f4e77d36d62c // indirect
-	golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a // indirect
-	google.golang.org/grpc v1.26.0
+	google.golang.org/grpc v1.38.0
 )
 
 go 1.13