Update close handler to avoid unhandled promise rejections

Author: clue

src/EventSource.php

@@ -270,6 +270,8 @@ public function close()
 
             $request->then(function (ResponseInterface $response) {
                 $response->getBody()->close();
+            }, function () {
+                // ignore to avoid reporting unhandled rejection
             });
             $request->cancel();
         }