fixed typos

UPGRADE-2.8.md

@@ -181,7 +181,7 @@ Form
    {
        public function getExtendedType()
        {
-           method_exists(AbstractType::class, 'getBlockPrefix') ? FormType::class : 'form';
+           return method_exists(AbstractType::class, 'getBlockPrefix') ? FormType::class : 'form';
        }
    }
    ```

src/Symfony/Component/Form/AbstractType.php

@@ -74,7 +74,7 @@ abstract class AbstractType implements FormTypeInterface
     /**
      * Returns the prefix of the template block name for this type.
      *
-     * The block prefixes defaults to the underscored short class name with
+     * The block prefixes default to the underscored short class name with
      * the "Type" suffix removed (e.g. "UserProfileType" => "user_profile").
      *
      * @return string The prefix of the template block name