Clean-up DC Sponsorship
Clean-up DC Sponsorship

* Markdown instead of HTML
* Gold Sponsorships are sold out, too.

Signed-off-by: Nathen Harvey <nharvey@chef.io>

Former-commit-id: 817b0e2d365486bddf7640f39fdd39bdf45390f5
gomex/devopsdays-web,gomex/devopsdays-web,gomex/devopsdays-web,gomex/devopsdays-web