Fix revision

As mentioned in #42, setting a default revision to 1 breaks strict '=' dependency checks in DEB packages (I haven't tested it with RPMs). This was also reported as an issue and removed in fpm itself a while ago (see jordansissel/fpm#5).

As an example, you can use the fpm-cookery-gem recipe : ftw depends on http_parser.rb version 0.5.3 and the generated DEBs won't install if revision is set to 1 by default.

This pull requests removes the default value and updates version code and tests accordingly. It also updates the fpm-cookery-gem recipe (version updates and new systemu recipe in the chain).