增加发券规则

app/Admin/Controllers/Activity/IndexController.php

@@ -204,7 +204,7 @@ class IndexController extends AdminController
             if ($request->total < 0) {
                 $error = new MessageBag([
                     'title'   => '错误',
-                    'message' => '可发券总数必须大于0',
+                    'message' => '可发券总数必须大于0.',
                 ]);
 
                 return back()->withInput()->with(compact('error'));