Fix ConsiderUsingStaticTypeRule rule for Hash

This makes the Hash class a static class, fixing a Gendarme static analysis rule:

http://www.flibitijibibo.com/fna/gendarme_nonet.html#ConsiderUsingStaticTypeRule
https://github.com/spouliot/gendarme/wiki/Gendarme.Rules.Design.ConsiderUsingStaticTypeRule%282.10%29

This change should have no functional difference.