Update composer.json for PHP 7.2

vendor/guzzlehttp/guzzle/src/MessageFormatterInterface.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace GuzzleHttp;
+
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+interface MessageFormatterInterface
+{
+    /**
+     * Returns a formatted message string.
+     *
+     * @param RequestInterface       $request  Request that was sent
+     * @param ResponseInterface|null $response Response that was received
+     * @param \Throwable|null        $error    Exception that was received
+     */
+    public function format(RequestInterface $request, ?ResponseInterface $response = null, ?\Throwable $error = null): string;
+}