Fix 0 download issue with monthly download shield (#5426)

README.md

@@ -3,7 +3,7 @@
 <p align="center">
   <a href="https://circleci.com/gh/vuejs/vue/tree/dev"><img src="https://img.shields.io/circleci/project/vuejs/vue/dev.svg" alt="Build Status"></a>
   <a href="https://codecov.io/github/vuejs/vue?branch=dev"><img src="https://img.shields.io/codecov/c/github/vuejs/vue/dev.svg" alt="Coverage Status"></a>
-  <a href="https://www.npmjs.com/package/vue"><img src="https://img.shields.io/npm/dt/vue.svg" alt="Downloads"></a>
+  <a href="https://www.npmjs.com/package/vue"><img src="https://img.shields.io/npm/dm/vue.svg" alt="Downloads"></a>
   <a href="https://www.npmjs.com/package/vue"><img src="https://img.shields.io/npm/v/vue.svg" alt="Version"></a>
   <a href="https://www.npmjs.com/package/vue"><img src="https://img.shields.io/npm/l/vue.svg" alt="License"></a>
   <br>