Use RbConfig instead of deprecated Config

[luislavena]

Hello,

Thank you for Padrino!

I've started to play with it against 1.9.3 (coming out next month) and found a warning when using padrino command, that is comment from padrino-core.

$ padrino g
/Users/luis/.rvm/gems/ruby-1.9.3-head/gems/padrino-core-0.10.0/lib/padrino-core/command.rb:19: Use RbConfig instead of obsolete and deprecated Config.
Please specify generator to use (project, app, mailer, controller, model, migration, plugin)

The root is the usage of Config instead of RbConfig here:
https://github.com/padrino/padrino-framework/blob/master/padrino-core/lib/padrino-core/command.rb#L19-20

Thank you.