chore(format): change by gofumpt tool (#697)

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

core/stringx/strings.go

@@ -86,7 +86,7 @@ func Reverse(s string) string {
 }
 
 // Substr returns runes between start and stop [start, stop) regardless of the chars are ascii or utf8.
-func Substr(str string, start int, stop int) (string, error) {
+func Substr(str string, start, stop int) (string, error) {
 	rs := []rune(str)
 	length := len(rs)