Remove unused import

Author: Minishlink

src/WebPush.php

@@ -16,7 +16,6 @@
 use Base64Url\Base64Url;
 use GuzzleHttp\Client;
 use GuzzleHttp\Exception\RequestException;
-use GuzzleHttp\Promise\Promise;
 use GuzzleHttp\Psr7\Request;
 use Psr\Http\Message\ResponseInterface;