Ignore metadata attributes in AsciiDoc

[ariebonn]

I have AsciiDoc files with the following header:

= Title
:description: My page description.
:keywords: keyword 1,keyword 2,keyword 3

I would like Vale to ignore the line starting with :keywords:. I tried to use TokenIgnores, but it doesn't seem to be working.
This is my config:

StylesPath = styles
MinAlertLevel = suggestion
Packages = proselint, AsciiDoc
IgnoredScopes = code, tt, img, url, a
SkippedScopes = script, style, pre, figure, code, listingblock, literalblock

[asciidoctor]
experimental = NO

[docs/[!.]*.adoc]
BasedOnStyles = Vale
TokenIgnores = (:keywords:.+[^\n])

Would appreciate any ideas.