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.

backend/hubic/hubic.go

@@ -9,6 +9,7 @@ package hubic
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"net/http"
@@ -16,7 +17,6 @@ import (
 	"time"
 
 	swiftLib "github.com/ncw/swift/v2"
-	"github.com/pkg/errors"
 	"github.com/rclone/rclone/backend/swift"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config/configmap"
@@ -120,7 +120,7 @@ func (f *Fs) getCredentials(ctx context.Context) (err error) {
 	if resp.StatusCode < 200 || resp.StatusCode > 299 {
 		body, _ := ioutil.ReadAll(resp.Body)
 		bodyStr := strings.TrimSpace(strings.Replace(string(body), "\n", " ", -1))
-		return errors.Errorf("failed to get credentials: %s: %s", resp.Status, bodyStr)
+		return fmt.Errorf("failed to get credentials: %s: %s", resp.Status, bodyStr)
 	}
 	decoder := json.NewDecoder(resp.Body)
 	var result credentials
@@ -146,7 +146,7 @@ func (f *Fs) getCredentials(ctx context.Context) (err error) {
 func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, error) {
 	client, _, err := oauthutil.NewClient(ctx, name, m, oauthConfig)
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to configure Hubic")
+		return nil, fmt.Errorf("failed to configure Hubic: %w", err)
 	}
 
 	f := &Fs{
@@ -163,7 +163,7 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 	}
 	err = c.Authenticate(ctx)
 	if err != nil {
-		return nil, errors.Wrap(err, "error authenticating swift connection")
+		return nil, fmt.Errorf("error authenticating swift connection: %w", err)
 	}
 
 	// Parse config into swift.Options struct