adds fix for custom props on track requests (#291)

Author: cykolln

KlaviyoV3Sdk/KlaviyoV3Api.php

@@ -432,15 +432,18 @@ public function buildCustomerProperties($customerProperties)
 
         $data = array(
             self::TYPE_KEY_PAYLOAD => self::PROFILE_KEY_PAYLOAD,
-            self::ATTRIBUTE_KEY_PAYLOAD => $kl_properties,
-            self::PROPERTIES => $customerProperties,
+            self::ATTRIBUTE_KEY_PAYLOAD => $kl_properties
         );
 
         if (isset($customerProperties['$id'])) {
             $data[self::ID_KEY_PAYLOAD] = $customerProperties['$id'];
             unset($customerProperties['$id']);
         }
 
+        if(!empty($customerProperties)) {
+            $data[self::ATTRIBUTE_KEY_PAYLOAD][self::PROPERTIES] = $customerProperties;
+        }
+
         return array(
             self::PROFILE_KEY_PAYLOAD => array(
                 self::DATA_KEY_PAYLOAD => $data