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

plugins/php-imap/vendor/nikic/php-parser/lib/PhpParser/Builder.php

@@ -0,0 +1,12 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser;
+
+interface Builder {
+    /**
+     * Returns the built node.
+     *
+     * @return Node The built node
+     */
+    public function getNode(): Node;
+}