FileSystem driver now tries to create cache folder before throwing InvalidArgumentException

Hello

Fixes https://github.com/tedivm/TedivmStashBundle/issues/15

This is a very small change allowing `FileSystem` driver to try to create the cache folder if it doesn't already exist. If folder creation fails, then the exception is thrown.

Note the usage of the silent operator (`@`). It's here only to avoid a verbose warning if folder creation fails since we want to throw an exception.