Use the disc list style type (#683)

Previously, it was the `circle` list style type, but it was determined
that the `disc` list style type is in many ways a better match for Rust.

Author: camelid

src/styles/app.scss

@@ -189,6 +189,10 @@ ul, ol {
   padding-left: 1.2em;
 }
 
+ul {
+  list-style-type: disc;
+}
+
 .posts {
   background-color: $gray;
   color: white;