Replace errorFormat for error-format, changed in phpstan v0.11

Author: Carles Mata

lint/linter/PhpstanLinter.php

@@ -87,7 +87,7 @@ protected function getMandatoryFlags()
         $flags = array(
             'analyse',
             '--no-progress',
-            '--errorFormat=checkstyle'
+            '--error-format=checkstyle'
         );
         if (null !== $this->configFile) {
             array_push($flags, '-c', $this->configFile);