fixed php-coveralls usage

.travis.yml

@@ -19,4 +19,4 @@ script:
   - vendor/bin/phpunit --coverage-clover=coverage.clover
   - vendor/bin/phpcs -p --standard=PSR2 --ignore=vendor/ ./
 after_script:
-  - travis_retry php vendor/bin/coveralls
\ No newline at end of file
+  - travis_retry php vendor/bin/php-coveralls
\ No newline at end of file

composer.json

@@ -17,9 +17,9 @@
     },
     "require-dev": {
         "elasticsearch/elasticsearch": "^6.0",
-        "phpunit/phpunit": "^6.0",
+        "phpunit/phpunit": "~6.0",
         "squizlabs/php_codesniffer": "^3.0",
-        "php-coveralls/php-coveralls": "~2.0"
+        "php-coveralls/php-coveralls": "^2.1"
     },
     "suggest": {
       "elasticsearch/elasticsearch": "This library is for elasticsearch/elasticsearch client to enhance it with DSL functionality."

phpunit.xml.dist

@@ -35,6 +35,7 @@
 
     <logging>
         <log type="coverage-text" target="php://stdout" showOnlySummary="true"/>
+        <log type="coverage-php" target="coverage.cov"/>
     </logging>
 
 </phpunit>