When no one wins, display a message about the result being a draw

src/index.js

@@ -2,10 +2,6 @@ import React from 'react';
 import ReactDOM from 'react-dom';
 import './index.css';
 
-/*TODO
-
-    When no one wins, display a message about the result being a draw.
-*/
 
 function Square(props) {
     const classNames = ['square'];
@@ -156,6 +152,11 @@ function calculateWinState(squares) {
             return {winner: squares[a], line: lines[i]};
         }
     }
+
+    if (squares.every(square => !!square)) {
+        return {winner: 'Draw :/', line: []};
+    }
+
     return null;
 }