Feature/fix keymap

Hi,
Just a quick fix for a bug I found when encrypting. Looks like the recent 0.3 patch doesn't map the recipient keys correctly leading to the following error,

/Library/Ruby/Gems/1.8/gems/hiera-eyaml-gpg-0.3/lib/hiera/backend/eyaml/encryptors/gpg.rb:108:in `encrypt': undefined local variable or method `key' for Hiera::Backend::Eyaml::Encryptors::Gpg:Class (NameError)
        from /Library/Ruby/Gems/1.8/gems/hiera-eyaml-gpg-0.3/lib/hiera/backend/eyaml/encryptors/gpg.rb:106:in `map'
        from /Library/Ruby/Gems/1.8/gems/hiera-eyaml-gpg-0.3/lib/hiera/backend/eyaml/encryptors/gpg.rb:106:in `encrypt'
        from /Library/Ruby/Gems/1.8/gems/hiera-eyaml-1.3.8/lib/hiera/backend/eyaml/parser/encrypted_tokens.rb:20:in `decrypted_value'
        from /Library/Ruby/Gems/1.8/gems/hiera-eyaml-1.3.8/lib/hiera/backend/eyaml/parser/encrypted_tokens.rb:120:in `create_token'
        from /Library/Ruby/Gems/1.8/gems/hiera-eyaml-1.3.8/lib/hiera/backend/eyaml/parser/parser.rb:71:in `parse_sca