fix(README): replace travis and appveyor badges with GH actions (#1282)

Author: czosel

README.md

@@ -12,11 +12,8 @@
 <h2 align="center">Prettier PHP Plugin</h2>
 
 <p align="center">
-  <a href="https://travis-ci.org/prettier/plugin-php/">
-    <img alt="Travis" src="https://img.shields.io/travis/prettier/plugin-php/master.svg?style=flat-square&label=Travis+CI">
-  </a>
-  <a href="https://ci.appveyor.com/project/prettier/plugin-php">
-    <img alt="AppVeyor Build Status" src="https://img.shields.io/appveyor/ci/prettier/plugin-php.svg?style=flat-square&label=AppVeyor">
+  <a href="https://github.com/prettier/plugin-php/actions">
+    <img alt="GitHub Workflow Status" src="https://img.shields.io/github/workflow/status/prettier/plugin-php/Node CI?style=flat-square">
   </a>
   <a href="https://www.npmjs.com/package/@prettier/plugin-php">
     <img alt="npm version" src="https://img.shields.io/npm/v/@prettier/plugin-php.svg?style=flat-square">