Add CircleCI badge

Author: mglaman

README.md

@@ -1,6 +1,6 @@
 # phpstan-drupal
 
-[![Build Status](https://travis-ci.com/mglaman/phpstan-drupal.svg?branch=master)](https://travis-ci.com/mglaman/phpstan-drupal)
+[![Build Status](https://travis-ci.com/mglaman/phpstan-drupal.svg?branch=master)](https://travis-ci.com/mglaman/phpstan-drupal) [![CircleCI](https://circleci.com/gh/mglaman/phpstan-drupal.svg?style=svg)](https://circleci.com/gh/mglaman/phpstan-drupal)
 
 Extension for [PHPStan](https://github.com/phpstan/phpstan) to allow analysis of Drupal code.