remove PHP 7.2 deprecated each call

Author: fbourigault

DependencyInjection/HttplugExtension.php

@@ -274,7 +274,8 @@ private function configureClient(ContainerBuilder $container, $clientName, array
 
         $plugins = [];
         foreach ($arguments['plugins'] as $plugin) {
-            list($pluginName, $pluginConfig) = each($plugin);
+            $pluginName = key($plugin);
+            $pluginConfig = current($plugin);
             if ('reference' === $pluginName) {
                 $plugins[] = $pluginConfig['id'];
             } elseif ('authentication' === $pluginName) {