Merge pull request #2111 from tugascript/graphql-15

Add graphql version ^15

Author: kamilmysliwiec

content/graphql/quick-start.md

@@ -9,7 +9,7 @@ In this chapter, we assume a basic understanding of GraphQL, and focus on how to
 Start by installing the required packages:
 
 ```bash
-$ npm i @nestjs/graphql graphql apollo-server-express
+$ npm i @nestjs/graphql graphql@^15 apollo-server-express
 ```
 
 > info **Hint** If using Fastify, instead of installing `apollo-server-express`, you should install `apollo-server-fastify`.