Add key to table element arrays

src/BottomRow.tsx

@@ -7,10 +7,10 @@ export function BottomRow(props: BottomRowProps) {
   const { wordLength, totalScore } = props;
   const cells = Array(wordLength)
     .fill(0)
-    .map(() => <td className="Row-letter hidden" />);
+    .map((_, i) => <td key={i} className="Row-letter hidden" />);
 
   return (
-    <tr className="Bottom-Row" data-row-score={totalScore}>
+    <tr key="bottom" className="Bottom-Row" data-row-score={totalScore}>
       {cells}
     </tr>
   );