Suppress USWDS color token errors

[drew-usds]

#485 updated UWDS to 2.4.0 and moved our color variables into non-uswds, brand-specific colors. 2.4.0 allows this now, where presently it only let you use specific color tokens.

Presently, building the site locally spits out the below error per overridden color token:

WARNING: Override: `#122d44` is not a USWDS color token.
         on line 916 of /Users/adgardner/usds/website/assets/uswds-sass/core/_functions.scss, in `color'
         from line 288 of /Users/adgardner/usds/website/assets/uswds-sass/core/_variables.scss
         from line 16 of an unknown file

USWDS claims you can suppress the errors, but I wasn't able to get it to work.