feat: 增加 iconv 帮助函数、更换 fetch 帮助函数

src/utils/fetch.ts

@@ -1,3 +1,3 @@
-import fetch from 'flyio';
+const superagent = require('superagent');
 
-export default fetch;
+export default superagent;

src/utils/iconv.ts

@@ -0,0 +1,3 @@
+const iconv = require("iconv-lite");
+
+export default iconv;