Fix property visibility in ObjectPropertyHydrator example

ObjectPropertyHydrator example should probably consist of publicly accessible properties, as opposed to ReflectionHydrator.

Signed-off-by: Michał Kurzydłowski <[email protected]>

docs/book/v4/quick-start.md

@@ -97,10 +97,10 @@ The ObjectPropertyHydrator hydrates objects and extracts data using publicly acc
 ```php
 class User
 {
-    private $firstName;
-    private $lastName;
-    private $emailAddress;
-    private $phoneNumber;
+    public $firstName;
+    public $lastName;
+    public $emailAddress;
+    public $phoneNumber;
 }
 
 $data = [