bump google.golang.org/grpc v1.20.1

full diff: https://github.com/grpc/grpc-go/compare/v1.12.2...v1.20.1

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/google.golang.org/grpc/resolver/passthrough/passthrough.go

@@ -45,7 +45,7 @@ type passthroughResolver struct {
 }
 
 func (r *passthroughResolver) start() {
-	r.cc.NewAddress([]resolver.Address{{Addr: r.target.Endpoint}})
+	r.cc.UpdateState(resolver.State{Addresses: []resolver.Address{{Addr: r.target.Endpoint}}})
 }
 
 func (*passthroughResolver) ResolveNow(o resolver.ResolveNowOption) {}