Fix method for adding placholders in progressBar

The method is called setPlaceholderFormatterDefinition and not setPlaceholderFormatter

Author: danez

components/console/helpers/progressbar.rst

@@ -289,7 +289,7 @@ display that are not available in the list of built-in placeholders, you can
 create your own. Let's see how you can create a ``remaining_steps`` placeholder
 that displays the number of remaining steps::
 
-    ProgressBar::setPlaceholderFormatter(
+    ProgressBar::setPlaceholderFormatterDefinition(
         '%remaining_steps%',
         function (ProgressBar $bar, OutputInterface $output) {
             return $bar->getMaxSteps() - $bar->getStep();