The <Story>.saveHash() method was removed from Snowman v2.0 and its functionality was merged into the <Story>.save() method. It no longer exists, so it still being referred to in places within the v2.0 source code—in comments, specifically—and in the documentation are errors.
I’m unsure why Dan removed it. While it was only used internally by <Story>.save(), it was also useful for external code to offer a better save experience than Snowman does natively, so its removal seems bizarre.