Use stable version of satooshi/php-coveralls

Author: Martins Sipenko

composer.json

@@ -16,7 +16,7 @@
     "require": {
         "php": ">=5.3",
         "guzzle/guzzle": ">=3.0",
-        "satooshi/php-coveralls": "dev-master",
+        "satooshi/php-coveralls": ">=0.6.1",
         "symfony/console": ">=2.0"
     },
     "require-dev": {