create data dir before copy

server/server.js

@@ -53,8 +53,8 @@ const sslCert = process.env.SSL_CERT || args["ssl-cert"] || undefined;
 // Data Directory (must be end with "/")
 Database.dataDir = process.env.DATA_DIR || args["data-dir"] || "./data/";
 Database.path = Database.dataDir + "kuma.db";
-if (! fs.existsSync(this.dataDir)) {
+if (! fs.existsSync(Database.dataDir)) {
-    fs.mkdirSync(this.dataDir, { recursive: true });
+    fs.mkdirSync(Database.dataDir, { recursive: true });
 }
 console.log(`Data Dir: ${Database.dataDir}`);