bug symfony#6787 Fix reference to output object (micheal)

This PR was submitted for the 3.1 branch but it was merged into the 2.7 branch instead (closes symfony#6787). Discussion ---------- Fix reference to output object `$this` does not have a `writeln` method on it, but `$output` does. Commits ------- 4deb3f0 Fix reference to output object

Author: weaverryan

console.rst

@@ -131,7 +131,7 @@ Use input options or arguments to pass information to the command::
  ]);
 
  // retrieve the argument value using getArgument()
- $this->writeln('Username: '.$input->getArgument('username'));
+ $output->writeln('Username: '.$input->getArgument('username'));
  }
 
 Now, you can pass the username to the command: