Removing use of deprecated method ProgressBar->getStep from Download Command

Changing min symfony/console version because of deprecated functions

Author: jzawadzki

composer.json

@@ -15,7 +15,7 @@
     "require": {
         "php": ">=5.4.0",
         "guzzlehttp/guzzle": "~5.0",
-        "symfony/console": "~2.5",
+        "symfony/console": "~2.6",
         "symfony/filesystem": "~2.5",
         "raulfraile/distill": "~0.9,!=0.9.3,!=0.9.4"
     },

src/Symfony/Installer/DownloadCommand.php

@@ -102,7 +102,7 @@ protected function download()
                     return $this->formatSize($bar->getMaxSteps());
                 });
                 ProgressBar::setPlaceholderFormatterDefinition('current', function (ProgressBar $bar) {
-                    return str_pad($this->formatSize($bar->getStep()), 11, ' ', STR_PAD_LEFT);
+                    return str_pad($this->formatSize($bar->getProgress()), 11, ' ', STR_PAD_LEFT);
                 });
 
                 $progressBar = new ProgressBar($this->output, $downloadSize);