Update dependencies + two minor fixups

[htvennik]

Update dependencies in composer.json. Looks like things work without further modifications.

I added two very small fixups as well:

• use put instead of write so the file will be updated if it is already present on the external storage
• use listContents instead of listFiles so it also works without the ListFiles plugin.

[htvennik]

Ping @Nyholm

Build is failing on PHP 5.x only because of reaching memory limit while running composer.