修复seeder错误；删除第三方的think迁移工具，在extend中重新实现；

extend/phinx/Migration/IrreversibleMigrationException.php

@@ -0,0 +1,20 @@
+<?php
+
+/**
+ * MIT License
+ * For full license information, please view the LICENSE file that was distributed with this source code.
+ */
+
+namespace Phinx\Migration;
+
+use Exception;
+
+/**
+ * Exception class thrown when migrations cannot be reversed using the 'change'
+ * feature.
+ *
+ * @author Rob Morgan <robbym@gmail.com>
+ */
+class IrreversibleMigrationException extends Exception
+{
+}