调整升级

1.更改了electron和nsis镜像地址。
2.升级了electron到20.0.3， 修改了新版romote的处理方式。
3.增加了canvas右键菜单功能。
4.Explorer显示纵向滚动条。

render-process/TreeTabs.tsx

@@ -1,7 +1,7 @@
 import Editor from "./Editor";
 import React, { Component } from "react";
 import { Layout, Tabs, message } from "antd";
-import { ipcRenderer, remote } from "electron";
+import { ipcRenderer } from "electron";
 import * as path from "path";
 
 import "antd/dist/antd.dark.css";