Fix import express graphql tutorial (graphql#893)

Co-authored-by: Alexandre Alencar <[email protected]>

Author: aalencar

site/graphql-js/Tutorial-ExpressGraphQL.md

@@ -17,7 +17,7 @@ Let's modify our “hello world” example so that it's an API server rather tha
 
 ```javascript
 var express = require('express');
-var graphqlHTTP = require('express-graphql');
+var { graphqlHTTP } = require('express-graphql');
 var { buildSchema } = require('graphql');
 
 // Construct a schema, using GraphQL schema language