Fix context in quickstart (#772)

Author: ctjhoa

docs/book/content/quickstart.md

@@ -114,7 +114,7 @@ struct Mutation;
 impl Mutation {
 
     fn createHuman(context: &Context, new_human: NewHuman) -> FieldResult<Human> {
-        let db = executor.context().pool.get_connection()?;
+        let db = context.pool.get_connection()?;
         let human: Human = db.insert_human(&new_human)?;
         Ok(human)
     }