Error on first step of tutorial

Hi,

Following this tutorial (https://www.howtographql.com/graphql-js/1-getting-started/)  will lead to the following error when trying to run the server:

> Error: Must provide document.

As a beginner I did not really understood the issue, but it can be fixed by going to a more recent version of apollo-server instead of the version 2 used in the tutorial:
`"apollo-server": "^3.4.0",`