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

plugins/php-imap/vendor/psr/simple-cache/src/CacheException.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Psr\SimpleCache;
+
+/**
+ * Interface used for all types of exceptions thrown by the implementing library.
+ */
+interface CacheException extends \Throwable
+{
+}