Fix incorrect count of empty cells

fix #197

Author: phil-r

index.js

@@ -24,10 +24,10 @@ const chunk = (arr, n) =>
 
 const prepareData = ({ data, numColumns, itemsPerRow }) => {
   const col = numColumns || itemsPerRow;
-  const missing = data.length % col;
+  const missing = (col - (data.length % col)) % col;
   return [
     ...data,
-    ...Array.from(Array(col - missing)).map(() => ({ __empty: true }))
+    ...Array.from(Array(missing)).map(() => ({ __empty: true }))
   ];
 };