Fix method for adding placholders in progressBar

The method is called setPlaceholderFormatterDefinition and not setPlaceholderFormatter

see [here][1]

Edit:
I found another glitch: The name of the placeholder must not be packed in %-characters, like it is the case when using the placeholders in the format. As you can see [here][2] the defaults are also not like this and best indication:  it does not work if doing like in the docs :) 

[1]: https://github.com/symfony/symfony/blob/2.5/src/Symfony/Component/Console/Helper/ProgressBar.php#L82

[2]: https://github.com/symfony/symfony/blob/2.5/src/Symfony/Component/Console/Helper/ProgressBar.php#L486