Added PHPStan

Author: Steveb-p

tests/lib/Output/Generator/JsonTest.php

@@ -208,6 +208,7 @@ public function testGeneratorHashElement()
 
         $generator->startHashElement('elements');
 
+        \Phpstan\dumpType($generator);
         $generator->startValueElement('element', 'element value 1', ['attribute' => 'attribute value 1']);
         $generator->endValueElement('element');