fix struct tags (#7)

model/transfer.go

@@ -2,7 +2,7 @@ package model
 
 type Transfer struct {
 	Common
-	ServerID uint64
-	In       uint64
-	Out      uint64
+	ServerID uint64 `json:"server_id"`
+	In       uint64 `json:"in"`
+	Out      uint64 `json:"out"`
 }