Update Google fonts to remove unused weight and CSS API v2.
Update Google fonts to remove unused weight and CSS API v2.

The 300 weight of Source Code Pro is not used anywhere.  This change
also updates to using Google Fonts CSS API v2 and specifying
display=swap to avoid a "flash of invisible text".

Resolves #241

alexandrevicenzi/Flex,alexandrevicenzi/Flex,alexandrevicenzi/Flex,alexandrevicenzi/Flex