fix(导图): Array.map 传递多参数导致 ancestors 默认值失效

.map(toElixirNode) 传递 (item, index, array) 三个参数，
index 作为数字覆盖 ancestors 默认值 []，导致 [...ancestors] 报错。
改为箭头函数只传第一个参数。

src/components/MindMapViewer.vue

@@ -103,7 +103,7 @@ const toElixirData = (tree: MindMapTreeNode): MindElixirData => {
     nodeData: {
       id: "root",
       topic: tree.title || "思维导图",
-      children: (tree.children || []).map(toElixirNode),
+      children: (tree.children || []).map(c => toElixirNode(c)),
     },
   } as MindElixirData;
 };