Fixed affix-bottom positioning

Set top position to (scrollHeight - this.$element.height() - offsetBottom).

js/affix.js

@@ -82,7 +82,7 @@
       .trigger($.Event(affixType.replace('affix', 'affixed')))
 
     if (affix == 'bottom') {
-      this.$element.offset({ top: position.top })
+      this.$element.offset({ top: scrollHeight - this.$element.height() - offsetBottom })
     }
   }