Fixes gemspec

Virtus has been updated to 1.0

including Virtus module is deprecated. Use 'include Virtus.model' instead /home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive/support/json_model.rb:42:in `include'
/home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive/support/node.rb:15: warning: toplevel constant Object referenced by Virtus::Attribute::Object
/home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive/support/node_list.rb:14: warning: toplevel constant Object referenced by Virtus::Attribute::Object
rake aborted!
undefined method `primitive' for AdaptivePayments::NodeList:Class
/home//.rvm/gems/ruby-1.9.3-p392/gems/attr_encrypted-1.2.1/lib/attr_encrypted.rb:241:in `method_missing'
/home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive/support/node_list.rb:15:in `<class:NodeList>'
/home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive/support/node_list.rb:14:in `<module:AdaptivePayments>'
/home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive/support/node_list.rb:3:in `<top (required)>'
/home//.rvm/gems/ruby-1.9.3-p392/gems/backports-3.3.5/lib/backports/tools.rb:328:in `require'
/home//.rvm/gems/ruby-1.9.3-p392/gems/backports-3.3.5/lib/backports/tools.rb:328:in `require_with_backports'
/home//.rvm/gems/ruby-1.9.3-p392/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
/home//.rvm/gems/ruby-1.9.3-p392/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
/home//.rvm/gems/ruby-1.9.3-p392/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
/home//.rvm/gems/ruby-1.9.3-p392/bundler/gems/pp-adaptive-ca05e65cd853/lib/pp-adaptive.rb:9:in `<top (required)>'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler/runtime.rb:72:in `require'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler/runtime.rb:72:in `block (2 levels) in require'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler/runtime.rb:70:in `each'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler/runtime.rb:70:in `block in require'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler/runtime.rb:59:in `each'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler/runtime.rb:59:in `require'
/home//.rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.3.1/lib/bundler.rb:132:in `require'