Use Duration.Truncate for truncating precision (#2711)

`Duration.Truncate` was added in Go 1.9 and Gin required Go version 1.13+ now.
So we can use `Duration.Truncate`.

Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

logger.go

@@ -138,8 +138,7 @@ var defaultLogFormatter = func(param LogFormatterParams) string {
 	}
 
 	if param.Latency > time.Minute {
-		// Truncate in a golang < 1.8 safe way
-		param.Latency = param.Latency - param.Latency%time.Second
+		param.Latency = param.Latency.Truncate(time.Second)
 	}
 	return fmt.Sprintf("[GIN] %v |%s %3d %s| %13v | %15s |%s %-7s %s %#v\n%s",
 		param.TimeStamp.Format("2006/01/02 - 15:04:05"),