Downgrade log level to debug (#22)

diff --git a/lib/skywalking/client.lua b/lib/skywalking/client.lua
index 42b8f7f..7312a26 100644
--- a/lib/skywalking/client.lua
+++ b/lib/skywalking/client.lua
@@ -231,7 +231,7 @@
     end
 
     if count > 0 then
-        log(ERR, count,  " segments reported.")
+        log(DEBUG, count,  " segments reported.")
     end
 end