fix CS, use regex class from new mongodb extension

src/Jenssegers/Mongodb/Validation/DatabasePresenceVerifier.php

 <?php namespace Jenssegers\Mongodb\Validation;
 
+use MongoDB\BSON\Regex as MongoRegex;
+
 class DatabasePresenceVerifier extends \Illuminate\Validation\DatabasePresenceVerifier
 {
     /**
@@ -40,7 +42,7 @@ class DatabasePresenceVerifier extends \Illuminate\Validation\DatabasePresenceVe
     public function getMultiCount($collection, $column, array $values, array $extra = [])
     {
         foreach ($values as &$value) {
-            $value = new \MongoRegex("/$value/i");
+            $value = new MongoRegex("/$value/i");
         }
         
         $query = $this->table($collection)->whereIn($column, $values);