fix bug and add service file

1.修正列印大小無法寫入BUG
2.加入SYSTEMD系統服務腳本

initscript/systemd/ble-server.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=BLE Printer Server
+
+[Service]
+ExecStart=/usr/bin/node /usr/local/node/ble-server/app.js
+Restart=always
+User=root
+Environment="NODE_ENV=production"
+
+[Install]
+WantedBy=multi-user.target