docs: 更新版本号

njuthesis.tex

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 % NJU Thesis Undergraduate
 % 南京大学本科生毕业论文LaTeX模板
-% Version 0.3.0 (2021-09-09)
+% Version 0.4.0 (2021-09-10)
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 % 请关注项目地址以获取最新变化
 % https://github.com/nju-lug/NJUThesisUndergraduate