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

extend/think/migration/command/stubs/seed.stub

@@ -0,0 +1,19 @@
+<?php
+
+use think\migration\Seeder;
+
+class SeederClass extends Seeder
+{
+    /**
+     * Run Method.
+     *
+     * Write your database seeder using this method.
+     *
+     * More information on writing seeders is available here:
+     * http://docs.phinx.org/en/latest/seeding.html
+     */
+    public function run()
+    {
+
+    }
+}