lesson update and save not working

[manojkumarbehera]

on lesson update getting this error
EditLessonComponent.html:5 ERROR TypeError: this.sdkDb.update is not a function
at LessonsService.webpackJsonp.65.LessonsService.firebaseUpdate (lessons.service.ts:92)

[jaroslaw-bagnicki]

In constructor of LessonsService class should be:
this.sdkDb = fb.database().**ref()**;