Use phpstan.neon as default (#7)

Even though we fetch getProjectConfigFile from the $analysisResult, it's best to fallback to the standard filename.

In our own projects, we use phpstan.php, but that's not the standard.

Author: ruudk

src/TicketSwapErrorFormatter.php

@@ -57,7 +57,7 @@ public function formatErrors(AnalysisResult $analysisResult, Output $output) : i
             );
         }
 
-        $projectConfigFile = 'phpstan.php';
+        $projectConfigFile = 'phpstan.neon';
         if ($analysisResult->getProjectConfigFile() !== null) {
             $projectConfigFile = $this->relativePathHelper->getRelativePath($analysisResult->getProjectConfigFile());
         }