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

plugins/php-imap/vendor/sebastian/cli-parser/src/exceptions/AmbiguousOptionException.php

@@ -0,0 +1,26 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/cli-parser.
+ *
+ * (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\CliParser;
+
+use function sprintf;
+use RuntimeException;
+
+final class AmbiguousOptionException extends RuntimeException implements Exception
+{
+    public function __construct(string $option)
+    {
+        parent::__construct(
+            sprintf(
+                'Option "%s" is ambiguous',
+                $option
+            )
+        );
+    }
+}