优化

@@ -151,7 +151,7 @@ class Body {
             }
 
             if(!$data->get('content-type')){
-                $data->set('content-type','text/html');
+                $data->set('content-type','text/plain');
             }
 
             $this->items[] = $this->bodyDeCode($data);
@@ -188,7 +188,7 @@ class Body {
 
             $data->body = $text;
             if(!$data->get('content-type')){
-                $data->set('content-type','text/html');
+                $data->set('content-type','text/plain');
             }
             $this->items[] = $this->bodyDeCode($data);
         }