Version 0.7.0

[ehannes]

It's time to release a new version. From our new changelog:

Added

• Adds build test for Ruby 2.6.0, 2.6.3 and 2.7.0-preview.

Removed

• Drops support for Ruby < 2.4.0 since they are deprecated

Fixed

• Country attribute for Invoice and Order is now validated correctly.
• Fixes deprecation warnings

[ehannes]

@d-Pixie we should add all releases to GitHub. There are several missing ones. Compare the releases at https://rubygems.org/gems/fortnox-api/versions with https://github.com/accodeing/fortnox-api/releases