Bundler fails unless sinatra is already installed.

The `dubai.gemspec` file requires `dubai.rb`, and this breaks unless all dependencies are 
already installed. E.g. a `bundle install` in a vanilla install breaks with 

    There was a LoadError while evaluating dubai.gemspec:
    cannot load such file -- sinatra/base from
    blah blah ..../bundler/gems/dubai-918236eaa64b/dubai.gemspec:3:in `<main>'


Gemspec only needs version, so split it into a separate file and include that only. 

Also bumped the version, 0.0.1 -> 0.0.2; not sure if that's okay.