Changing test case and samples to use newer camelcase setters

sample/payments/ExecutePayment.php

@@ -25,7 +25,7 @@ if(isset($_GET['success']) && $_GET['success'] == 'true') {
 	// The payer_id is added to the request query parameters
 	// when the user is redirected from paypal back to your site
 	$execution = new PaymentExecution();
-	$execution->setPayer_id($_GET['PayerID']);
+	$execution->setPayerId($_GET['PayerID']);
 	
 	//Execute the payment
 	// (See bootstrap.php for more on `ApiContext`)
@@ -37,4 +37,4 @@ if(isset($_GET['success']) && $_GET['success'] == 'true') {
 	
 } else {
 	echo "User cancelled payment.";
-}
+}