Replace deprecated ioutil

As of Go 1.16, the same functionality is now provided by package io or
package os, and those implementations should be preferred in new code.

backend/drive/drive.go

@@ -14,9 +14,9 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"mime"
 	"net/http"
+	"os"
 	"path"
 	"regexp"
 	"sort"
@@ -1108,7 +1108,7 @@ func createOAuthClient(ctx context.Context, opt *Options, name string, m configm
 
 	// try loading service account credentials from env variable, then from a file
 	if len(opt.ServiceAccountCredentials) == 0 && opt.ServiceAccountFile != "" {
-		loadedCreds, err := ioutil.ReadFile(env.ShellExpand(opt.ServiceAccountFile))
+		loadedCreds, err := os.ReadFile(env.ShellExpand(opt.ServiceAccountFile))
 		if err != nil {
 			return nil, fmt.Errorf("error opening service account credentials file: %w", err)
 		}
@@ -3800,7 +3800,7 @@ func (o *linkObject) Open(ctx context.Context, options ...fs.OpenOption) (in io.
 		data = data[:limit]
 	}
 
-	return ioutil.NopCloser(bytes.NewReader(data)), nil
+	return io.NopCloser(bytes.NewReader(data)), nil
 }
 
 func (o *baseObject) update(ctx context.Context, updateInfo *drive.File, uploadMimeType string, in io.Reader,

backend/drive/drive_internal_test.go

@@ -7,7 +7,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"mime"
 	"os"
 	"path"
@@ -78,7 +77,7 @@ var additionalMimeTypes = map[string]string{
 // Load the example export formats into exportFormats for testing
 func TestInternalLoadExampleFormats(t *testing.T) {
 	fetchFormatsOnce.Do(func() {})
-	buf, err := ioutil.ReadFile(filepath.FromSlash("test/about.json"))
+	buf, err := os.ReadFile(filepath.FromSlash("test/about.json"))
 	var about struct {
 		ExportFormats map[string][]string `json:"exportFormats,omitempty"`
 		ImportFormats map[string][]string `json:"importFormats,omitempty"`