Remove the vendor directory in .gitignore as these dependencies are needed for php-imap

plugins/php-imap/vendor/sebastian/diff/src/Output/DiffOutputBuilderInterface.php

@@ -0,0 +1,19 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/diff.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Diff\Output;
+
+/**
+ * Defines how an output builder should take a generated
+ * diff array and return a string representation of that diff.
+ */
+interface DiffOutputBuilderInterface
+{
+    public function getDiff(array $diff): string;
+}