fix version and simplify gemspec

@latortuga
There are important files written to `man` and `build` also. If you just [want to remove version.rb from cleanup](https://github.com/burke/zeus/commit/119bb3ad565d0e8e6efac79e4d5efa7cd4444be8), and commit it, I can merge that, but I'm not taking untested build process refactors.