SetDefaultCommand first arg is command name

Author: mickaelandrieu

components/console/single_command_tool.rst

@@ -53,7 +53,7 @@ Of course, you can still register a command as usual::
   
   $application->add($command);
   
-  $application->setDefaultCommand($command, true); 
+  $application->setDefaultCommand($command->getName(), true); 
   $application->run();
   
 .. tip::