APIWrapper: Make mapDonation() static becauts it's called static

CRM/TwingleCampaign/Utils/APIWrapper.php

@@ -103,12 +103,12 @@ class CRM_TwingleCampaign_Utils_APIWrapper {
    * the de.systopia.twingle extension can include the campaign into the
    * contribution which it will create.
    *
-   * @param $apiRequest
-   * @param $callsame
+   * @param array $apiRequest
+   * @param callable $callsame
    *
    * @return mixed
    */
-  public function mapDonation($apiRequest, $callsame) {
+  public static function mapDonation(array $apiRequest, callable $callsame) {
 
     if (array_key_exists(
       'campaign_id',