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/Util/Literal.php

@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * MIT License
+ * For full license information, please view the LICENSE file that was distributed with this source code.
+ */
+
+namespace Phinx\Util;
+
+class Literal
+{
+    /**
+     * @var string The literal's value
+     */
+    protected $value;
+
+    /**
+     * @param string $value The literal's value
+     */
+    public function __construct(string $value)
+    {
+        $this->value = $value;
+    }
+
+    /**
+     * @return string Returns the literal's value
+     */
+    public function __toString(): string
+    {
+        return $this->value;
+    }
+
+    /**
+     * @param string $value The literal's value
+     * @return self
+     */
+    public static function from(string $value): Literal
+    {
+        return new self($value);
+    }
+}