Add proper .sops extension for file without extension

[randrusiak]

Story/Issue Link

Fixes #11

Background

Currently, if you add a file without an extension then ".sops" extension is added as a prefix. It looks strange and disallows adding a file with a local path for example ./file_no_ext. I added a simple conditional which handle this case :)

Versioning

Patch version

Additional Requests to Reviewers

Tasks

• [ ] Specs written
• [x] Manual testing