Fix default workspace in gen-dockerfile builder (#284)

Author: chingor13

builder/gen-dockerfile/src/GenFilesCommand.php

@@ -70,7 +70,7 @@ protected function initialize(InputInterface $input, OutputInterface $output)
             ?: self::DEFAULT_BASE_IMAGE;
         $this->workspace = $input->getOption('workspace')
             ?: getenv('PWD')
-            ?: self::DEFAULT_YAML_PATH;
+            ?: self::DEFAULT_WORKSPACE;
         $yamlPath = getenv('GAE_APPLICATION_YAML_PATH')
             ?: self::DEFAULT_YAML_PATH;
         if (file_exists($this->workspace . '/' . $yamlPath)) {