Fix load_config cannot render erb lines.

[gizipp]

Patch for #21.

So we can do

production:
  client_key: <%= ENV['VERITRANS_CLIENT_KEY'] %>
  server_key: <%= ENV['VERITRANS_SERVER_KEY'] %>
  api_host: <%= ENV['VERITRANS_API_HOST'] %>

in veritrans.yml

Thanks

[Paxa]

Very good, thank you!