Heading levels show line heights of .5 over what is documented

[anselmbradford]

Describe the bug

Visit https://cfpb.github.io/design-system/foundation/headings and inspect the web heading levels and check the computed styles and see that the line-heights are .5 higher than what's documented

@natalia-fitzgerald @jenn-franklin

[jenn-franklin]

I've made a note of this in our audit.

[Scotchester]

:wave:

A little historical context: I remember us intentionally making the decision to set all heading line heights to 1.25 for simplicity. I feel like it's likely that the documented line heights were simplified as a result, to avoid documenting a decimal value, but I could be mistaken.