docs(readme): fix build status badge

Author: Guillaume Chau

README.md

@@ -3,7 +3,7 @@
 [![npm](https://img.shields.io/npm/v/vue-apollo.svg) ![npm](https://img.shields.io/npm/dm/vue-apollo.svg)](https://www.npmjs.com/package/vue-apollo)
 [![vue1](https://img.shields.io/badge/apollo-2.x-blue.svg)](https://www.apollographql.com/)
 [![vue1](https://img.shields.io/badge/vue-1.x-brightgreen.svg) ![vue2](https://img.shields.io/badge/vue-2.2+-brightgreen.svg)](https://vuejs.org/)
-[![CircleCI branch](https://img.shields.io/circleci/project/github/Akryum/vue-apollo/master.svg)](https://circleci.com/gh/Akryum/vue-apollo/tree/master)
+[![CircleCI branch](https://img.shields.io/circleci/project/github/Akryum/vue-apollo/dev.svg)](https://circleci.com/gh/Akryum/vue-apollo/tree/dev)
 
 <p align="center">
   <img src="https://cdn-images-1.medium.com/max/800/1*H9AANoofLqjS10Xd5TwRYw.png">