Fix gRPC query service cmux

breaking change: grpc/grpc-go#2406
workaround described in:
- soheilhy/cmux#64
- https://github.com/soheilhy/cmux#limitations

Signed-off-by: Christian Weichel <christian.weichel@typefox.io>

cmd/query/app/server.go

@@ -102,9 +102,7 @@ func (s *Server) Start() error {
 	// cmux server acts as a reverse-proxy between HTTP and GRPC backends.
 	cmuxServer := cmux.New(s.conn)
 
-	grpcListener := cmuxServer.Match(
-		cmux.HTTP2HeaderField("content-type", "application/grpc"),
-		cmux.HTTP2HeaderField("content-type", "application/grpc+proto"))
+	grpcListener := cmuxServer.MatchWithWriters(cmux.HTTP2MatchHeaderFieldSendSettings("content-type", "application/grpc"))
 	httpListener := cmuxServer.Match(cmux.Any())
 
 	go func() {