switch to Roboto web font (#22)

for now, at least. tired of waiting on Chromium to fix system fonts on Catalina.... https://bugs.chromium.org/p/chromium/issues/detail?id=1005969

Roboto seems closest to San Francisco.

assets/sass/main.scss

@@ -7,6 +7,7 @@
 @import 'abstracts/functions';
 
 // Global Styles
+@import 'components/webfonts';
 @import 'components/global';
 @import 'components/header';
 @import 'components/footer';