Remove the marker of menu <ul> element

This is a problem in Firefox because Firefox displays markers(bullet
points) of `<li>` element just before the inline contents of the
elements. But Chrome displays them before the element, not depending on
the content of the `<li>` element. So it wasn't visible on Chrome but
it's in Firefox. This CSS change will remove that in Firefox too.

static/css/style.css

@@ -183,6 +183,7 @@ img {
   padding-bottom: 180px;
   text-align: center;
   background: #fff;
+  list-style: none;
 }
 .menu li + li {
   margin-top: 12px;