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

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>

src/croc/croc.go

@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
 	"net"
 	"os"
@@ -1482,7 +1481,7 @@ func (c *Client) receiveData(i int) {
 					c.FilesToTransfer[c.FilesToTransferCurrentNum].FolderRemote,
 					c.FilesToTransfer[c.FilesToTransferCurrentNum].Name,
 				)
-				b, _ := ioutil.ReadFile(pathToFile)
+				b, _ := os.ReadFile(pathToFile)
 				fmt.Print(string(b))
 			}
 			log.Debug("sending close-sender")

src/croc/croc_test.go

@@ -1,7 +1,6 @@
 package croc
 
 import (
-	"io/ioutil"
 	"os"
 	"sync"
 	"testing"
@@ -153,7 +152,7 @@ func TestCrocLocal(t *testing.T) {
 
 func TestCrocError(t *testing.T) {
 	content := []byte("temporary file's content")
-	tmpfile, err := ioutil.TempFile("", "example")
+	tmpfile, err := os.CreateTemp("", "example")
 	if err != nil {
 		panic(err)
 	}