added php download of membershipments

vendor/illuminate/contracts/Database/Eloquent/SerializesCastableAttributes.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Illuminate\Contracts\Database\Eloquent;
+
+interface SerializesCastableAttributes
+{
+    /**
+     * Serialize the attribute when converting the model to an array.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model  $model
+     * @param  string  $key
+     * @param  mixed  $value
+     * @param  array  $attributes
+     * @return mixed
+     */
+    public function serialize($model, string $key, $value, array $attributes);
+}