Clean up completed multi curl instance to fix memory leak

src/Curl/MultiCurl.php

@@ -662,6 +662,7 @@ class MultiCurl
                             $ch->curlErrorCode = $info_array['result'];
                             $ch->exec($ch->curl);
 
+                            // Remove completed instance from active curls.
                             unset($this->activeCurls[$key]);
 
                             // Start a new request before removing the handle of the completed one.
@@ -670,6 +671,9 @@ class MultiCurl
                             }
                             curl_multi_remove_handle($this->multiCurl, $ch->curl);
 
+                            // Clean up completed instance.
+                            $ch->close();
+
                             break;
                         }
                     }