Use method instead of function

cmd/main.go

@@ -121,7 +121,7 @@ func main() {
 		}
 		matchIndices := make([]reg.Match, 0)
 		if matchNumFlagEnabled {
-			tmp, err := reg.FindNthMatch(regComp, test_str, *matchNum)
+			tmp, err := regComp.FindNthMatch(test_str, *matchNum)
 			if err == nil {
 				matchIndices = append(matchIndices, tmp)
 			}