[docs] Updated CI Status badge in README

[skip ci]

README.md

@@ -1,6 +1,6 @@
 # ansible-openwisp2
 
-[![Build Status](https://github.com/openwisp/ansible-openwisp2/workflows/Ansible%20OpenWISP2%20CI%20Build/badge.svg?branch=master)](https://github.com/openwisp/ansible-openwisp2/actions?query=workflow%3A%22Ansible+OpenWISP2+CI+Build%22)
+[![Ansible-OpenWISP2 CI Build](https://github.com/openwisp/ansible-openwisp2/actions/workflows/ci.yml/badge.svg)](https://github.com/openwisp/ansible-openwisp2/actions/workflows/ci.yml)
 [![Galaxy](http://img.shields.io/badge/galaxy-openwisp.openwisp2-blue.svg?style=flat-square)](https://galaxy.ansible.com/ui/standalone/roles/openwisp/openwisp2/)
 [![Chat](https://img.shields.io/gitter/room/nwjs/nw.js.svg)](https://gitter.im/openwisp/general)