Update the dependency on Guava

Hi,

Could you please apply this patch updating the dependency on Guava?  The latest version of Guava removed the `MapMaker.makeComputingMap()` method used by sisu-guice. It has been replaced by a new `CacheBuilder` class, see:

http://code.google.com/p/guava-libraries/wiki/MapMakerMigration
http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/cache/CacheBuilder.html

Thank you