Updated purchase receipt suitable for sending to apple verification server

(cherry picked from commit bd7192572697e919a8eb7cf6d8b44d699dae24c9)

platform/iphone/in_app_store.mm

@@ -207,7 +207,7 @@ Error InAppStore::restore_purchases() {
 
 				NSString *receipt_to_send = nil;
 				if (receipt != nil) {
-					receipt_to_send = [receipt description];
+					receipt_to_send = [receipt base64EncodedStringWithOptions:0];
 				}
 				Dictionary receipt_ret;
 				receipt_ret["receipt"] = String::utf8(receipt_to_send != nil ? [receipt_to_send UTF8String] : "");