Remove github.com/pkg/errors and replace with std library version

This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.

This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.

cmd/serve/docker/volume.go

@@ -2,14 +2,14 @@ package docker
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 	"runtime"
 	"sort"
 	"time"
 
-	"github.com/pkg/errors"
-
 	"github.com/rclone/rclone/cmd/mountlib"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config"
@@ -155,7 +155,7 @@ func (vol *Volume) checkMountpoint() error {
 	_, err := os.Lstat(path)
 	if os.IsNotExist(err) {
 		if err = file.MkdirAll(path, 0700); err != nil {
-			return errors.Wrapf(err, "failed to create mountpoint: %s", path)
+			return fmt.Errorf("failed to create mountpoint: %s: %w", path, err)
 		}
 	} else if err != nil {
 		return err
@@ -182,7 +182,7 @@ func (vol *Volume) setup(ctx context.Context) error {
 	_, mountFn := mountlib.ResolveMountMethod(vol.mountType)
 	if mountFn == nil {
 		if vol.mountType != "" {
-			return errors.Errorf("unsupported mount type %q", vol.mountType)
+			return fmt.Errorf("unsupported mount type %q", vol.mountType)
 		}
 		return errors.New("mount command unsupported by this build")
 	}
@@ -242,7 +242,7 @@ func (vol *Volume) clearCache() error {
 	}
 	root, err := VFS.Root()
 	if err != nil {
-		return errors.Wrapf(err, "error reading root: %v", VFS.Fs())
+		return fmt.Errorf("error reading root: %v: %w", VFS.Fs(), err)
 	}
 	root.ForgetAll()
 	return nil