Mention the minimum required bob.db.base version
The bob.db.base.FileDatabase class was introduced in bob.db.base 2.2.1:
https://github.com/bioidiap/bob.db.base/commit/b3e2273d3243a7c4adaded4129c50a86927f2724
The bob.db.base.FileDatabase class was introduced in bob.db.base 2.2.1:
https://github.com/bioidiap/bob.db.base/commit/b3e2273d3243a7c4adaded4129c50a86927f2724