Sort actual groups of gems

Ordinare now sorts gems in group {} blocks and similar like source {}. For example:

source "https://rubygems.org"

gemspec

# Auth
gem "devise"
gem "authenticator"

# Assets
gem "rails-assets"
gem "jquery"
gem "angular"

group :test do
  gem "webmock"
  gem "cucumber-rails"
end

After $ ordinare will look like this:

source "https://rubygems.org"

gemspec

# Auth
gem "authenticator"
gem "devise"

# Assets
gem "angular"
gem "jquery"
gem "rails-assets"

group :test do
  gem "cucumber-rails"
  gem "webmock"
end