`github-cache/` should be in `pharo-local/` in Pharo 6

[jecisc]

In Pharo 6 Esteban created a folder pharo-local/. This folder should contains all the Pharo files of an image excepted the .image and .changes. So, github-cache/ should be move in the folder.

To get the folder, one can use FileLocator localDirectory.