res channel causes connection.Run() to block When request timeout occuers (#167)

* Change the RPCResultChannel to a buffer channel to avoid blocking connection.Run() when request timeout occuers

Signed-off-by: dsmlily <dsmlily_2008@126.com>

* use 10 as the buffer size.

Signed-off-by: duansumin <duansumin@vipkid.com.cn>
diff --git a/pulsar/internal/rpc_client.go b/pulsar/internal/rpc_client.go
index dda701f..a0c4fad 100644
--- a/pulsar/internal/rpc_client.go
+++ b/pulsar/internal/rpc_client.go
@@ -90,7 +90,7 @@
 		*RPCResult
 		error
 	}
-	ch := make(chan Res)
+	ch := make(chan Res, 10)
 
 	// TODO: in here, the error of callback always nil
 	cnx.SendRequest(requestID, baseCommand(cmdType, message), func(response *pb.BaseCommand, err error) {