Let Folder class create files recursively to avoid errors.

mkdir() should leverage the "recursive" option by default.
It prevents errors and warnings like

    Warning: mkdir(): No such file or directory in E:\...\Plugin\Setup\vendor\cakephp\cakephp\src\Filesystem\Folder.php on line 538

when the subfolders of the tmp dir are not yet available, but could easily be created recursively here.

This fixed it.