Shipping preference misspelling.

PayPal v2 Orders API documentation has this enum option as the singular
"shipping_preference".

Author: TechhDan

Diff for: samples/AuthorizeIntentExamples/CreateOrder.php

@@ -25,7 +25,7 @@ private static function buildRequestBody()
                     'brand_name' => 'EXAMPLE INC',
                     'locale' => 'en-US',
                     'landing_page' => 'BILLING',
-                    'shipping_preferences' => 'SET_PROVIDED_ADDRESS',
+                    'shipping_preference' => 'SET_PROVIDED_ADDRESS',
                     'user_action' => 'PAY_NOW',
                 ),
             'purchase_units' =>

Diff for: samples/CaptureIntentExamples/CreateOrder.php

@@ -27,7 +27,7 @@ private static function buildRequestBody()
                     'brand_name' => 'EXAMPLE INC',
                     'locale' => 'en-US',
                     'landing_page' => 'BILLING',
-                    'shipping_preferences' => 'SET_PROVIDED_ADDRESS',
+                    'shipping_preference' => 'SET_PROVIDED_ADDRESS',
                     'user_action' => 'PAY_NOW',
                 ),
             'purchase_units' =>