upgraded coveralls client library

Author: Simonas Šerlinskas

Diff for: composer.json

@@ -19,7 +19,7 @@
         "elasticsearch/elasticsearch": "^6.0",
         "phpunit/phpunit": "^6.0",
         "squizlabs/php_codesniffer": "^3.0",
-        "satooshi/php-coveralls": "~1.0|~2.0"
+        "php-coveralls/php-coveralls": "~2.0"
     },
     "suggest": {
       "elasticsearch/elasticsearch": "This library is for elasticsearch/elasticsearch client to enhance it with DSL functionality."