Use Github actions badge in README

Author: martin-helmich

README.md

@@ -1,6 +1,6 @@
 # JSON assertions for PHPUnit
 
-[![Build Status](https://travis-ci.org/martin-helmich/phpunit-json-assert.svg)](https://travis-ci.org/martin-helmich/phpunit-json-assert)
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 [![Code Climate](https://codeclimate.com/github/martin-helmich/phpunit-json-assert/badges/gpa.svg)](https://codeclimate.com/github/martin-helmich/phpunit-json-assert)
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