Confirm reset

src/Board.tsx

@@ -49,11 +49,13 @@ class Board extends React.Component<{}, State> {
   };
 
   reset = () => {
-    this.setState({ grid: [...INITIAL_GRID] });
-    this.stop();
-    this.setState({ running: false });
-    this.setState({ cellSize: DEFAULT_CELL_SIZE });
-    this.setState({ width: DEFAULT_WIDTH, height: DEFAULT_HEIGHT });
+    if (window.confirm('Are you sure?')) {
+      this.setState({ grid: [...INITIAL_GRID] });
+      this.stop();
+      this.setState({ running: false });
+      this.setState({ cellSize: DEFAULT_CELL_SIZE });
+      this.setState({ width: DEFAULT_WIDTH, height: DEFAULT_HEIGHT });
+    }
   };
 
   toggleCell = (x: number, y: number) => {