Fix, detach with Objectid

Author: florianJacques

src/Relations/BelongsToMany.php

@@ -235,7 +235,11 @@ public function detach($ids = [], $touch = true)
         // If associated IDs were passed to the method we will only delete those
         // associations, otherwise all of the association ties will be broken.
         // We'll return the numbers of affected rows when we do the deletes.
-        $ids = (array) $ids;
+        if ($ids instanceof \MongoDB\BSON\ObjectId) {
+            $ids = [$ids];
+        } else {
+            $ids = (array) $ids;
+        }
 
         // Detach all ids from the parent model.
         if ($this->parent instanceof \MongoDB\Laravel\Eloquent\Model) {