[#25] tracing: Fix panic on closed channel

Closed channel is also ready for communication, so select
statement can write to it.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/tracing/grpc.go

@@ -51,7 +51,6 @@ func NewGRPCStreamClientInterceptor() grpc.StreamClientInterceptor {
 		strWrp := newgRPCClientStream(str, desc, finished, done)
 
 		go func() {
-			defer close(finished)
 			defer close(done)
 			defer span.End()