Fix bug where configuration file doesn't save

app.js

@@ -32,6 +32,7 @@ const options = commandLineArgs(optionDefinitions);
 global.syzoj = {
   rootDir: __dirname,
   config: require(options.config),
+  configDir: options.config,
   models: [],
   modules: [],
   db: null,

utility.js

@@ -363,6 +363,6 @@ module.exports = {
   },
   async saveConfig() {
     let fs = require('fs-extra');
-    fs.writeFileAsync(syzoj.rootDir + '/config.json', JSON.stringify(syzoj.config, null, 2));
+    fs.writeFileAsync(syzoj.configDir, JSON.stringify(syzoj.config, null, 2));
   }
 };