"Build a Musical Game using Oboe" Step 7 missing instructions to add scheduleSongEvents() to Game.h

In Step 7 of [Build a Musical Game using Oboe](https://codelabs.developers.google.com/codelabs/musicalgame-using-oboe/index.html?index=..%2F..%2Fio2018#6)

There is an instruction to add a function `void Game::scheduleSongEvents()` in Game.cpp without declaring it in Game.h