Enable link underline on hover for better UX

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/generic/typography.scss

@@ -40,7 +40,7 @@ a {
   outline: none;
   color: $link_color;
   &:hover {
-    text-decoration: none;
+    text-decoration: underline;
     color: $link_hover_color;
   }