修复链接无效的bug

Author: kuafuRace

README.en.md

@@ -179,7 +179,7 @@ carbon.Parse("2020-08-05 13:14:15").SetMinute(60).ToDateTimeString() // 2020-08-
 carbon.Parse("2020-08-05 13:14:15").SetSecond(10).ToDateTimeString() // 2020-08-05 13:14:10
 carbon.Parse("2020-08-05 13:14:15").SetSecond(60).ToDateTimeString() // 2020-08-05 13:15:00
 ```
-> For more timezone constants, please see the [const.go](./const.go) file
+> For more timezone constants, please see the [constant.go](./constant.go) file
 
 ##### Start and end
 ```go

README.md

@@ -178,7 +178,7 @@ carbon.Parse("2020-08-05 13:14:15").SetMinute(60).ToDateTimeString() // 2020-08-
 carbon.Parse("2020-08-05 13:14:15").SetSecond(10).ToDateTimeString() // 2020-08-05 13:14:10
 carbon.Parse("2020-08-05 13:14:15").SetSecond(60).ToDateTimeString() // 2020-08-05 13:15:00
 ```
->更多时区常量请查看[const.go](./const.go)文件
+>更多时区常量请查看[constant.go](./constant.go)文件
 
 ##### 开始时间、结束时间
 ```go