"Use Data" and "Publish Data" aren't centered between pipes in header

[robredpath]

On https://iati.github.io/design-system/?path=/docs/layout-header--docs:

I think Contact isn't centred against the page edge as well but that probably matters less given that it's a full-width element

[tillywoodfield]

@robredpath I've fixed this so the spacing is now even: https://iati.github.io/design-system/?path=/docs/components-header--docs