misc: bump nuclei sdk npk version to 0.8.1

Signed-off-by: Huaqi Fang <578567190@qq.com>

npk.yml

@@ -2,7 +2,7 @@
 ## This npk.yml only works with Nuclei Studio 2023.10 or later
 name: sdk-nuclei_sdk
 owner: nuclei
-version: 0.8.1-dev
+version: 0.8.1
 description: Nuclei Embedded Software Development Kit
 type: sdk
 keywords: