refactor: move from io/ioutil to io and os package (#1772)

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/image/image.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"image"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -247,7 +246,7 @@ func Serve(w http.ResponseWriter, r *http.Request, path string) {
 		}
 		defer rc.Close()
 
-		data, err := ioutil.ReadAll(rc)
+		data, err := io.ReadAll(rc)
 		if err != nil {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return