fix(react): ReactFlow comp ref type

examples/react/src/examples/CustomNode/index.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, MouseEvent, ChangeEvent, useCallback } from 'react';
+import { useState, useEffect, MouseEvent, ChangeEvent, useCallback, useRef } from 'react';
 import {
   ReactFlow,
   MiniMap,
@@ -45,6 +45,7 @@ const nodeTypes = {
 };
 
 const CustomNodeFlow = () => {
+  const ref = useRef(null);
   const [nodes, setNodes] = useState<MyNode[]>([]);
   const onNodesChange: OnNodesChange<MyNode> = useCallback(
     (changes) =>
@@ -165,6 +166,7 @@ const CustomNodeFlow = () => {
       minZoom={0.3}
       maxZoom={2}
       onBeforeDelete={onBeforeDelete}
+      ref={ref}
     >
       <MiniMap<MyNode>
         nodeStrokeColor={(n: MyNode): string => {