Fix text colors in Atom One Dark theme

The foreground color was accidentally set wrongly before (using
$foreground itself, which wasn't set yet) so that it ended up as full
white, which was too bright. These should be the right colors from the
theme.

tildes/scss/themes/_atom_one_dark.scss

@@ -2,8 +2,8 @@
 
 $background: hsl(220, 13%, 18%);
 $background-alt: #21242b;
-$foreground-alt: hsl(220, 14%, 71%);
-$foreground: lighten($foreground, 10%);
+$foreground: hsl(220, 14%, 71%);
+$foreground-alt: hsl(220, 9%, 55%);
 
 $cyan: hsl(187, 47%, 55%);
 $blue: hsl(207, 82%, 66%);