commands/plugin: Remove PruneGems
load with bundler context
fast path Vagrant --version
Lock to log4r < 1.1.11 because we got fucked

1.1.11 was released today and seriously broke backwards compatibility.
While they never officially made any promise to follow semver, it is
almost expected at this point, but log4r decided to just fuck that.

1.1.11 changed the arity of Log4r::Logger.initialize. That seriously
breaks _everything_.

Darwin awarddddddddd goes to...