New option to only update "proven" gems by date.

[chrismo]

If I use bundler-patch in an automated process to keep me up-to-date on patched gems, I may not want to use a new gem version the day after it's released. Maybe I'd like to be a week or a month behind, to give it time to "prove" itself.

Implementation on this would be sketchy depending on access to the gem's release date.