HTTP_UPDATE_FAILD错误（-5）：HTTP错误：连接丢失

Question

我正在尝试通过OTA更新NodeMCU上的固件。可以在GitHub上下载要下载并上传到Flash的bin文件。我正在使用NodeMCU Amica。

/**
   httpUpdate.ino

    Created on: 27.11.2015

*/

#include <Arduino.h>

#include <ESP8266WiFi.h>
#include <ESP8266WiFiMulti.h>

#include <ESP8266HTTPClient.h>
#include <ESP8266httpUpdate.h>

#define USE_SERIAL Serial

#ifndef APSSID
#define APSSID "Akhtar"
#define APPSK  "akhtar1234"
#endif

ESP8266WiFiMulti WiFiMulti;

void setup() {

  USE_SERIAL.begin(115200);
  // USE_SERIAL.setDebugOutput(true);

  USE_SERIAL.println();
  USE_SERIAL.println();
  USE_SERIAL.println();

  for (uint8_t t = 4; t > 0; t--) {
    USE_SERIAL.printf("[SETUP] WAIT %d...\n", t);
    USE_SERIAL.flush();
    delay(1000);
  }

  WiFi.mode(WIFI_STA);
  WiFiMulti.addAP(APSSID, APPSK);


}

void loop() {
  // wait for WiFi connection
  if ((WiFiMulti.run() == WL_CONNECTED)) {

    WiFiClient client;

    // The line below is optional. It can be used to blink the LED on the board during flashing
    // The LED will be on during download of one buffer of data from the network. The LED will
    // be off during writing that buffer to flash
    // On a good connection the LED should flash regularly. On a bad connection the LED will be
    // on much longer than it will be off. Other pins than LED_BUILTIN may be used. The second
    // value is used to put the LED on. If the LED is on with HIGH, that value should be passed
    ESPhttpUpdate.setLedPin(LED_BUILTIN, LOW);

    t_httpUpdate_return ret = ESPhttpUpdate.update(client, "https://github.com/akhtarusafzai/office/blob/master/Blink.bin");
    // Or:
    //t_httpUpdate_return ret = ESPhttpUpdate.update(client, "server", 80, "file.bin");

    switch (ret) {
      case HTTP_UPDATE_FAILED:
        USE_SERIAL.printf("HTTP_UPDATE_FAILD Error (%d): %s\n", ESPhttpUpdate.getLastError(), ESPhttpUpdate.getLastErrorString().c_str());
        break;

      case HTTP_UPDATE_NO_UPDATES:
        USE_SERIAL.println("HTTP_UPDATE_NO_UPDATES");
        break;

      case HTTP_UPDATE_OK:
        USE_SERIAL.println("HTTP_UPDATE_OK");
        break;
    }
  }
}

该代码应能下载文件，然后将其上传到设备Boot Loader。我的串行监视器上出现以下错误：

HTTP_UPDATE_FAILD Error (-5): HTTP error: connection lost