Added UID scope for OpenLDAP

- Closes #268

Author: stevebauman

src/Scopes/UidScope.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Adldap\Laravel\Scopes;
+
+use Adldap\Query\Builder;
+
+class UidScope implements ScopeInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function apply(Builder $builder)
+    {
+        $builder->whereHas($builder->getSchema()->userId());
+    }
+}