Face à un problème d'intégration de gmail avec ionic 3, obtention d'une erreur d'exécution >> L'objet (...) n'est pas une fonction

Je travaille avec ionic 3 où j'essaie d'intégrer google plus login dans mon application via firebase . Mais j'obtiens une erreur,

l'erreur est >>

{
  "name": "login",
  "version": "0.0.1",
  "author": "Ionic Framework",
  "homepage": "http://ionicframework.com/",
  "private": true,
  "scripts": {
    "start": "ionic-app-scripts serve",
    "clean": "ionic-app-scripts clean",
    "build": "ionic-app-scripts build",
    "lint": "ionic-app-scripts lint"
  },
  "dependencies": {
    "@angular/animations": "5.2.11",
    "@angular/common": "5.2.11",
    "@angular/compiler": "5.2.11",
    "@angular/compiler-cli": "5.2.11",
    "@angular/core": "5.2.11",
    "@angular/fire": "^5.1.1",
    "@angular/forms": "5.2.11",
    "@angular/http": "5.2.11",
    "@angular/platform-browser": "5.2.11",
    "@angular/platform-browser-dynamic": "5.2.11",
    "@ionic-native/core": "^3.6.1",
    "@ionic-native/google-plus": "^5.0.0",
    "@ionic-native/splash-screen": "~4.18.0",
    "@ionic-native/status-bar": "~4.18.0",
    "@ionic/storage": "2.2.0",
    "angularfire2": "^5.1.1",
    "cordova-android": "7.1.4",
    "cordova-plugin-device": "^2.0.2",
    "cordova-plugin-googleplus": "7.0.0",
    "cordova-plugin-ionic-keyboard": "^2.1.3",
    "cordova-plugin-ionic-webview": "^3.1.1",
    "cordova-plugin-splashscreen": "^5.0.2",
    "cordova-plugin-statusbar": "^2.4.2",
    "cordova-plugin-whitelist": "^1.3.3",
    "firebase": "^5.8.2",
    "ionic-angular": "3.9.2",
    "ionicons": "3.0.0",
    "rxjs": "5.5.11",
    "sw-toolbox": "3.6.0",
    "zone.js": "0.8.29"
  },
  "devDependencies": {
    "@ionic/app-scripts": "3.2.1",
    "typescript": "~2.6.2"
  },
  "description": "An Ionic project",
  "cordova": {
    "plugins": {
      "cordova-plugin-googleplus": {
        "REVERSED_CLIENT_ID": ".com.googleusercontent.apps.556482052199-f7848gi58u5h89lf2fvs99h5prk2vlbe"
      },
      "cordova-plugin-whitelist": {},
      "cordova-plugin-statusbar": {},
      "cordova-plugin-device": {},
      "cordova-plugin-splashscreen": {},
      "cordova-plugin-ionic-webview": {
        "ANDROID_SUPPORT_ANNOTATIONS_VERSION": "27.+"
      },
      "cordova-plugin-ionic-keyboard": {}
    },
    "platforms": [
      "android"
    ]
  }
}

fichier .ts

XXX

Code .html

<button style='    margin: 30px;
padding: 19px;
background: tomato;' ion-buttons icon-left (click)='login()' block outline><ion-icon name="logo-googleplus"> Login with google </ion-icon></button>

**** Package.json ****

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { GooglePlus } from '@ionic-native/google-plus/ngx';
import firebase from 'firebase';

/**
 * Generated class for the HomePage page.
 *
 * See https://ionicframework.com/docs/components/#navigation for more info on
 * Ionic pages and navigation.
 */

@IonicPage()
@Component({
  selector: 'page-home',
  templateUrl: 'home.html',
})
export class HomePage {

  constructor(public navCtrl: NavController, public navParams: NavParams  ,private googleplus: GooglePlus ) {
  }

  ionViewDidLoad() {
    console.log('ionViewDidLoad HomePage');
  }

  login(){
      this.googleplus.login({

        'webClientId':"556482052199-f7848gi58u5h89lf2fvs99h5prk2vlbe.apps.googleusercontent.com",
        'offline':true

      }).then(res =>{
        firebase.auth().signInWithCredential(firebase.auth.GoogleAuthProvider.credential(res.idToken)).then(suc=>{
          alert('login successful');
        }).catch(ns=> {
          alert('not successful');
        })
      })
  }



}

Pour plus d'informations, j'ai suivi le tutoriel youtube 1. Google Authentication ionic 2 & 3 avec Firebase - Le moyen le plus simple pour l'authentification Google https://www.youtube.com/watch?v=g_UGNO3IfN8 p >

2. http://edupala.com/ionic-3-gmail- login-with-firebase /

Mais j'obtiens la même erreur à chaque fois error >> ERROR TypeError: Object (...) n'est pas une fonction