Update coveralls dependency

Author: chadicus

.travis.yml

@@ -15,4 +15,4 @@ before_script:
   - composer update $PREFER_LOWEST
 script:
   - ./vendor/bin/phpunit
-after_success: ./vendor/bin/coveralls -v
+after_success: ./vendor/bin/php-coveralls -v

composer.json

@@ -22,6 +22,6 @@
     "require-dev": {
         "squizlabs/php_codesniffer": "^3.2",
         "phpunit/phpunit": "^6.5",
-        "php-coveralls/php-coveralls": "^1.0"
+        "php-coveralls/php-coveralls": "^2.1"
     }
 }