Fix descending sort being non-deterministic

Descending sort would sort differently for the same data on rerender for items that evaluated to the same value.

src/utils.js

@@ -80,7 +80,7 @@ function orderBy (arr, funcs, dirs) {
     }
     return dirs[0]
       ? a.__index - b.__index
-      : b.__index - b.__index
+      : b.__index - a.__index
   })
 }