fastlane: Error with posting data with 0x00FA character

Original issue by @chrisvire - Imported from fastlane/supply#26

We are trying to post a full description with accented u (0x00FA).

https://dl.dropboxusercontent.com/u/4049729/github/supply/full_description.txt

However, supply fails when google-api-client tries to encode as US-ASCII (even though it is trying to load metadata for language ‘es-419’). Do I need to create the file differently?

[17:59:26]: Loading metadata for language 'es-419'...
/var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client/request.rb:342:in `encode': "\xFA" on US-ASCII (Encoding::InvalidByteSequenceError)
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client/request.rb:342:in `to_json'
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client/request.rb:342:in `serialize_body'
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client/request.rb:93:in `initialize'
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client.rb:556:in `new'
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client.rb:556:in `generate_request'
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client.rb:621:in `execute!'
    from /var/lib/gems/2.0.0/gems/google-api-client-0.8.6/lib/google/api_client.rb:679:in `execute'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/client.rb:180:in `update_listing_for_language'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/listing.rb:25:in `save'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/uploader.rb:36:in `upload_metadata'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/uploader.rb:16:in `block in perform_upload'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/uploader.rb:11:in `foreach'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/uploader.rb:11:in `perform_upload'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/commands_generator.rb:37:in `block (2 levels) in run'
    from /var/lib/gems/2.0.0/gems/commander-4.3.5/lib/commander/command.rb:178:in `call'
    from /var/lib/gems/2.0.0/gems/commander-4.3.5/lib/commander/command.rb:178:in `call'
    from /var/lib/gems/2.0.0/gems/commander-4.3.5/lib/commander/command.rb:153:in `run'
    from /var/lib/gems/2.0.0/gems/commander-4.3.5/lib/commander/runner.rb:428:in `run_active_command'
    from /var/lib/gems/2.0.0/gems/commander-4.3.5/lib/commander/runner.rb:68:in `run!'
    from /var/lib/gems/2.0.0/gems/commander-4.3.5/lib/commander/delegates.rb:15:in `run!'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/commands_generator.rb:55:in `run'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/lib/supply/commands_generator.rb:15:in `start'
    from /var/lib/gems/2.0.0/gems/supply-0.2.2/bin/supply:6:in `<top (required)>'
    from /usr/local/bin/supply:23:in `load'
    from /usr/local/bin/supply:23:in `<main>'