Remove references to GuzzleHttp\Promise\rejection_for (Guzzle 7.7 com…

…patibility)

Fixes: gmponos#48

src/LogMiddleware.php

@@ -112,11 +112,11 @@ private function handleFailure(RequestInterface $request, array $options): calla
         return function (\Exception $reason) use ($request, $options) {
             if ($reason instanceof RequestException && $reason->hasResponse() === true) {
                 $this->handler->log($this->logger, $request, $reason->getResponse(), $reason, $this->stats, $options);
-                return \GuzzleHttp\Promise\rejection_for($reason);
+                return new \GuzzleHttp\Promise\RejectedPromise($reason);
             }
 
             $this->handler->log($this->logger, $request, null, $reason, $this->stats, $options);
-            return \GuzzleHttp\Promise\rejection_for($reason);
+            return new \GuzzleHttp\Promise\RejectedPromise($reason);
         };
     }