FORMAT.md is outdated

[Hugo4IT]

I noticed that FORMAT.md is missing the dataVersion property in the Header section. I made this an issue instead of a pull request with a fix because it's a simple fix but I'm unsure if it is preferred to put something in the Notes column about it only being included from version 6 onwards. I haven't checked anything else about the FORMAT.md, I just noticed this property missing while debugging something in my project.