Make the burger look right

• Make burger use the 4 spans as specified by bulma docs.
• Correct the burger animation to use those 4 spans
• Color the burger white

sass/_menu.scss

@@ -76,8 +76,12 @@
   #navbar-logo > img {
     filter: saturate(0) brightness(0) invert(1);
   }
+  #navbar-logo > img:hover {
+    filter: none;
+  }
 }
 
+// FIXME: https://github.com/jgthms/bulma/issues/3757
 .navbar-burger {
     color: white !important;
 }