chore(getting-started): fix "Variables and Mixins" section
chore(getting-started): fix "Variables and Mixins" section

Import statements were a little off

[#97135788]

sjolicoeur/pivotal-ui,sjolicoeur/pivotal-ui,CanopyCloud/pivotal-ui,pivotal-cf/pivotal-ui,npm/pivotal-ui,CanopyCloud/pivotal-ui,sjolicoeur/pivotal-ui,npm/pivotal-ui,CanopyCloud/pivotal-ui,pivotal-cf/pivotal-ui,pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui,npm/pivotal-ui