fix sessions.ErrNotFound.Equal example

Former-commit-id: 292eadaea9df1c680e68a3f92f86c8bf1edc2d7d

Author: kataras

_examples/sessions/database/badger/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"time"
 
 	"github.com/kataras/iris/v12"
@@ -90,9 +91,9 @@ func main() {
 	app.Get("/update", func(ctx iris.Context) {
 		// updates resets the expiration based on the session's `Expires` field.
 		if err := sess.ShiftExpiration(ctx); err != nil {
-			if sessions.ErrNotFound.Equal(err) {
+			if errors.Is(err, sessions.ErrNotFound) {
 				ctx.StatusCode(iris.StatusNotFound)
-			} else if sessions.ErrNotImplemented.Equal(err) {
+			} else if errors.Is(err, sessions.ErrNotImplemented) {
 				ctx.StatusCode(iris.StatusNotImplemented)
 			} else {
 				ctx.StatusCode(iris.StatusNotModified)