refactor: move from io/ioutil to io and os packages

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

Reference: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

logtail/example/logreprocess/logreprocess.go

@@ -9,7 +9,7 @@ import (
 	"bufio"
 	"encoding/json"
 	"flag"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"os"
@@ -50,7 +50,7 @@ func main() {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != 200 {
-		b, err := ioutil.ReadAll(resp.Body)
+		b, err := io.ReadAll(resp.Body)
 		if err != nil {
 			log.Fatalf("logreprocess: read error %d: %v", resp.StatusCode, err)
 		}