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>

core/endpoint.go

@@ -5,7 +5,7 @@ import (
 	"crypto/x509"
 	"encoding/json"
 	"errors"
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"net/url"
@@ -259,7 +259,7 @@ func (endpoint *Endpoint) call(result *Result) {
 		result.Connected = response.StatusCode > 0
 		// Only read the body if there's a condition that uses the BodyPlaceholder
 		if endpoint.needsToReadBody() {
-			result.body, err = ioutil.ReadAll(response.Body)
+			result.body, err = io.ReadAll(response.Body)
 			if err != nil {
 				result.AddError(err.Error())
 			}

core/endpoint_test.go

@@ -1,7 +1,7 @@
 package core
 
 import (
-	"io/ioutil"
+	"io"
 	"strings"
 	"testing"
 	"time"
@@ -245,7 +245,7 @@ func TestEndpoint_buildHTTPRequestWithGraphQLEnabled(t *testing.T) {
 	if contentType := request.Header.Get(ContentTypeHeader); contentType != "application/json" {
 		t.Error("request.Header.Content-Type should've been application/json, but was", contentType)
 	}
-	body, _ := ioutil.ReadAll(request.Body)
+	body, _ := io.ReadAll(request.Body)
 	if !strings.HasPrefix(string(body), "{\"query\":") {
 		t.Error("request.body should've started with '{\"query\":', but it didn't:", string(body))
 	}