Add php-coveralls dependency

Author: sandrokeil

composer.json

@@ -18,6 +18,7 @@
     "require-dev": {
         "infection/infection": "^0.11.0",
         "malukenho/docheader": "^0.1.7",
+        "php-coveralls/php-coveralls": "^2.1",
         "phpstan/phpstan": "^0.10.5",
         "phpstan/phpstan-strict-rules": "^0.10.1",
         "phpunit/phpunit": "^7.0.1",