Rename children directories before parent in renameSubFolders

[bancer]

Fixes #279.

[ADmad]

Using the RecursiveIteratorIterator::CHILD_FIRST flag when creating the iterator instance should avoid having to manually sort the paths.

[bancer]

    protected function renameSubFolders(string $path): void
    {
        $this->io->out("Moving sub directories of <info>$path</info>");
        if ($this->args->getOption('dry-run')) {
            return;
        }

        $folders = ['Layout', 'Element', 'Cell', 'Email', 'Plugin', 'Flash'];

        foreach ($folders as $folder) {
            $dirIter = new RecursiveDirectoryIterator(
                $path,
                RecursiveDirectoryIterator::UNIX_PATHS
            );
            $iterIter = new RecursiveIteratorIterator($dirIter,  RecursiveIteratorIterator::CHILD_FIRST);
            $templateDirs = new RegexIterator(
                $iterIter,
                '#/' . $folder . '/\.$#',
                RecursiveRegexIterator::SPLIT
            );

            foreach ($templateDirs as $val) {
                $this->renameWithCasing(
                    $val[0] . '/' . $folder,
                    $val[0] . '/' . strtolower($folder)
                );
            }
        }
    }

This with RecursiveIteratorIterator::CHILD_FIRST did not work for me. Still got "PHP Fatal error: Uncaught UnexpectedValueException: RecursiveDirectoryIterator::__construct(/path/to/project/templates/Layout/Email): Failed to open directory: No such file or directory in /path/to/upgrade/src/Command/FileRenameCommand.php:210" error.