Logger reference fix

Me again :) Thanks for fixing the gem versions in the gemspec.

Two more quick fixes I needed to get this to work with Ruby 2.1.2 via Capistrano. The tests were passing, but I received error running via Capistrano 2.15.5 - those tasks are hard to test in the Capistrano context!

*  Used a conventional module definition structure in Capistrano::S3::Publisher - for some reason it was seeing Capistrano::S3 as an uninitialized constant.
* Changed the initialization of Logger to explicitly refer to the root context Logger to avoid a name conflict with Capistrano::Logger - this was throwing an exception because their initializers are different.

Now the tests pass, and it works with Capistrano.

Thanks again,
BK