fix packet size issue

src/index.ts

@@ -240,6 +240,8 @@ export default class Updater {
 
                 // write file length
                 return new Promise((resolve, reject) => {
+                        // set mtu
+                        this.bleObject.requestMtu(this.bleDeviceId, this._packetSize, (mtu: number) => { this._packetSize = mtu}, () =>{ })
                         // start notify
                         this.bleObject.startNotification(this.bleDeviceId, this._updaterServiceUUID, this._updaterCommandCharacterisitcUUID,
                                 (rawData: ArrayBuffer): void => {