Issue fields in UTF-8 encoding are stored in uneditable format

Steps to reproduce ==================

1. Create an issue (via `ditz add`) with some nonASCII symbols put into any of its fields 2. Run `ditz edit <issue_id>`.

Expected behavior: ==================

All those fields are stored as I've typed them, to be readable and editable

Actual behavior: ================

Fields contain nonASCII chars are stored as `!binary` blobs (see issue issue 422d5361: Тестовая бага, для проверки поддержки UTF8 )

Notes =====

I'd also suggest this issue should be addressed to upstream YAML implementation but I'm not sure, since I'm not using Ruby.