All current dependencies should be declared as development

[arokettu]

Fix for #13

• Gemfile dependencies marked as :development so Jeweler adds them as development dependencies
• Version constraint for shoulda moved to Gemfile so no duplicate dependencies are generated
• Gemfile.lock is removed from repo and added to .gitignore. The file should not be committed for gems

I have tested rake gemspec:generate but not committed the new spec as it will be automatically regenerated by the Jeweler release procedure

p.s. Jeweler is deprecated https://github.com/technicalpickles/jeweler/issues/283 Have you thought of moving to Juwelier for example, or using pure Bundler?

[arokettu]

Fixed test failure on new rubies there's no more 'test/unit' in newer ruby versions so test-unit gem should be added