Fix logic that transform design tokens from json to sass variables

Summary

This PR fixes the logic for transforming design tokens for font sizes from json to sass variables

If this pull request requires a change to Emulsify documentation, those changes, updates, and/or new information must accompany this pull request.

[ ] Go to this file _token.scss
[ ] Confirm the following sass variables for font-sizes have the correct token value transformed into rem
--font-size-tiny;
--font-size-x-small
--font-size-caption
--font-size-small
--font-size-body
--font-size-lead
--font-size-h5
--font-size-h4
--font-size-h3
--font-size-h2
--font-size-h1
--font-size-display
--font-size-hero
--font-size-uber
--font-size-colossus
[ ] Run npm run develop
[ ] Go to http://localhost:6006/?path=/story/components-button--button or any other component, and confirm the font-size sass variable is a rem value

Closes #103