contexts should be versioned

Created by: nissimsan

This is a bug, given the context versioning which was just discussed on the call. Should be pointing at a versioned context: https://github.com/uncefact/spec-untp/pull/148/files#diff-4bbcb3ee3ac7bb4b1daebee238598ef0574447b6bdb59a82c90bbd54d509604d