Fix error message for Go 1.8.

Author: vmihailenco

options.go

@@ -3,6 +3,7 @@ package redis
 import (
 	"crypto/tls"
 	"errors"
+	"fmt"
 	"net"
 	"net/url"
 	"strconv"
@@ -151,7 +152,7 @@ func ParseURL(redisURL string) (*Options, error) {
 		o.DB = 0
 	case 1:
 		if o.DB, err = strconv.Atoi(f[0]); err != nil {
-			return nil, errors.New("invalid redis database number: " + err.Error())
+			return nil, fmt.Errorf("invalid redis database number: %q", f[0])
 		}
 	default:
 		return nil, errors.New("invalid redis URL path: " + u.Path)

options_test.go

@@ -63,7 +63,7 @@ func TestParseURL(t *testing.T) {
 		{
 			"redis://localhost/iamadatabase",
 			"",
-			0, false, errors.New("invalid redis database number: strconv.ParseInt: parsing \"iamadatabase\": invalid syntax"),
+			0, false, errors.New(`invalid redis database number: "iamadatabase"`),
 		},
 	}