Remove Net::SSH dependency for Ruby 1.9.3
Remove Net::SSH dependency for Ruby 1.9.3

Given Ruby 1.9.3 unsupported status, we do not want to limit fog
applications by limiting to older versions of `net-ssh`

If running on Ruby 1.9.3, please ensure your application is declaring
it's own dependency in it's `Gemfile`:

    gem "net-ssh", "< 3.0"

fog/fog-core