Move Cantarell before Ubuntu in font stack to fix GNOME + Ubuntu setups

Signed-off-by: Jan C. Borchardt <hey@jancborchardt.net>

core/css/variables.scss

@@ -83,7 +83,7 @@ $border-radius-large: 10px !default;
 // Pill-style button, value is large so big buttons also have correct roundness
 $border-radius-pill: 100px !default;
 
-$font-face: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen-Sans, Ubuntu, Cantarell, 'Helvetica Neue', Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol' !default;
+$font-face: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen-Sans, Cantarell, Ubuntu, 'Helvetica Neue', Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol' !default;
 
 $animation-quick: 100ms;
 $animation-slow: 300ms;