Log Message:
Update to 2.5.1

Upstream changes:
R6 2.5.1

    Removed unused packages from Suggests section in DESCRIPTION.

R6 2.5.0

    Resolved #195: Slightly clearer message when there is an error in the \ 
initialize() method.

    Fixed #214: When a non-portable object inheritance was cloned, methods that \ 
were inherited (and not overridden) had the wrong environment. (#215, #217)

    Printing R6 objects, no longer includes .__active__.