doc: Update badge in README.md (#118)

原来模糊的图片太违和了，还是改用了svg base64……

README.md

@@ -7,7 +7,7 @@
 
 Markdown 的轻量化特性，使您可以专注于论文内容而不用担心格式。书写时仅通过简单的标记，并通过替换样例模板中的个人信息，您就可以输出类 LaTeX 排版的精美论文与报告。本项目支持 Windows, macOS 和 Linux 三大平台的 Typora。
 
-<a href="https://github.com/Keldos-Li/typora-latex-theme/releases">![GitHub downloads](https://img.shields.io/github/downloads/Keldos-Li/typora-latex-theme/total?logo=data:image/png;base64,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)</a>
+<a href="https://github.com/Keldos-Li/typora-latex-theme/releases">![GitHub downloads](https://img.shields.io/github/downloads/Keldos-Li/typora-latex-theme/total?logo=data:image/svg+xml;base64,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)</a>
 <a href="https://github.com/Keldos-Li/typora-latex-theme/releases/latest">![GitHub release (latest by date including pre-releases)](https://img.shields.io/github/v/release/Keldos-Li/typora-latex-theme?include_prereleases&color=green&logo=hack-the-box)</a>
 <a href="https://github.com/Keldos-Li/typora-latex-theme/stargazers">![GitHub Repo stars](https://img.shields.io/github/stars/Keldos-Li/typora-latex-theme?style=flat&logo=github&color=yellow)</a>
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