docs: Update badge license link (#1794)

made license badge point to the respective file

Author: jamesgeorge007

README.md

@@ -7,7 +7,7 @@
 <p align="center">
   <a href="https://npmcharts.com/compare/vuepress?minimal=true"><a href="https://opencollective.com/vuepress" alt="Financial Contributors on Open Collective"><img src="https://opencollective.com/vuepress/all/badge.svg?label=financial+contributors" /></a> <img src="https://img.shields.io/npm/dm/vuepress.svg" alt="Downloads"></a>
   <a href="https://www.npmjs.com/package/vuepress"><img src="https://img.shields.io/npm/v/vuepress.svg" alt="Version"></a>
-  <a href="https://www.npmjs.com/package/vuepress"><img src="https://img.shields.io/npm/l/vuepress.svg" alt="License"></a>
+  <a href="https://github.com/vuejs/vuepress/blob/master/LICENSE"><img src="https://img.shields.io/npm/l/vuepress.svg" alt="License"></a>
   <a href="https://discordapp.com/invite/HBherRA"><img src="https://img.shields.io/badge/Discord-join%20chat-738bd7.svg" alt="vuepress channel on Discord"></a>
 </p>