Object(...) is not a function


#1

i am trying to receive firebase data inside my ionic app.

the .ts file is as follows

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { AngularFireDatabase } from 'angularfire2/database';
import { AddCommentPage } from '../add-comment/add-comment';
import { Review } from '../../models/review.interface';


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

  private ref =  this.database.list<Review>('reviews');
  constructor(public database: AngularFireDatabase ,public navCtrl: NavController, public navParams: NavParams) {
   
    this.ref.snapshotChanges().subscribe(console.log);

  }

  newComment(){
    this.navCtrl.push(AddCommentPage);
  }


}

my installed dependencies are

{
  "name": "app",
  "version": "0.0.1",
  "author": "Ionic Framework",
  "homepage": "http://ionicframework.com/",
  "private": true,
  "scripts": {
    "clean": "ionic-app-scripts clean",
    "build": "ionic-app-scripts build",
    "lint": "ionic-app-scripts lint",
    "ionic:build": "ionic-app-scripts build",
    "ionic:serve": "ionic-app-scripts serve"
  },
  "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/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": "4.7.0",
    "@ionic-native/in-app-browser": "^4.8.0",
    "@ionic-native/splash-screen": "4.7.0",
    "@ionic-native/status-bar": "4.7.0",
    "@ionic/storage": "2.1.3",
    "angularfire2": "^5.0.0-rc.11",
    "cordova-android": "7.0.0",
    "cordova-plugin-device": "^2.0.2",
    "cordova-plugin-inappbrowser": "^3.0.0",
    "cordova-plugin-ionic-keyboard": "^2.0.5",
    "cordova-plugin-ionic-webview": "^1.1.19",
    "cordova-plugin-splashscreen": "^5.0.2",
    "cordova-plugin-whitelist": "^1.3.3",
    "firebase": "^5.2.0",
    "ionic-angular": "3.9.2",
    "ionicons": "3.0.0",
    "rxjs": "^5.5.11",
    "sw-toolbox": "3.6.0",
    "zone.js": "0.8.26"
  },
  "devDependencies": {
    "@ionic/app-scripts": "3.1.10",
    "typescript": "~2.6.2"
  },
  "description": "An Ionic project",
  "cordova": {
    "plugins": {
      "cordova-plugin-whitelist": {},
      "cordova-plugin-device": {},
      "cordova-plugin-splashscreen": {},
      "cordova-plugin-ionic-webview": {},
      "cordova-plugin-ionic-keyboard": {},
      "cordova-plugin-inappbrowser": {}
    },
    "platforms": [
      "android"
    ]
  }
}

Please help me,
Its showing the above errors.