Update guava to 11.0.1 - match the version used by git-plugin

The latest guava version (16.0) causes test failures, so cannot be
used yet.  This version is consistent with the version used by
git-plugin which may avoid silent incompatibilities between the two
plugins.
Merge pull request #87 from MarkEWaite/master-update-guava-to-match-git-plugin

Update guava to 11.0.1 - match the version used by git-plugin