Avoid mixing stderr and stdout in outdated command as it mangles output

src/Composer/Command/ShowCommand.php

@@ -445,11 +445,10 @@ EOT
                     if (isset($package['path'])) {
                         $io->write(' ' . $package['path'], false);
                     }
+                    $io->write('');
                     if (isset($package['warning'])) {
-                        $io->writeError('');
-                        $io->writeError('<warning>' . $package['warning'] . '</warning>', false);
+                        $io->write('<warning>' . $package['warning'] . '</warning>');
                     }
-                    $io->write('');
                 }
 
                 if ($showAllTypes) {