Update chapters 05 and 06 (#81)

* Update chapter03-presenting-users.adoc

Fix: Use correct password_digest field in test code.
Fix: Typo.

* Update chapter03-presenting-users.adoc

Fix: Commit message for update action.

* Fix casing in create Order model statement

* Remove duplicated question from answers.

* Expose order model, not user model.

rails6/en/chapter06-improve-json.adoc

@@ -1099,11 +1099,6 @@ Which following snippet is a valid JSON:API response?:: With product's user into
 ----
 +
 
-What is the purpose of `Hash#dig` method?::
-  . Get a nested element safer.
-  . Get a nested element and load Active Record relations if needed.
-  . Add a nested element safer.
-
 What is the purpose of `Hash#dig` method?:: Get a nested element safer. It is a Ruby method allowing you to retrieve elements in a nested `Hash` by avoiding errors if an element is not present.
 
 How do you include user information in a JSON:API output of a product?::

rails6/en/chapter07-placing-orders.adoc

@@ -31,7 +31,7 @@ Let’s start by creating the older model with a special form:
 
 [source,bash]
 ----
-$ rails generate model order user:belongs_to total:decimal
+$ rails generate model Order user:belongs_to total:decimal
 ----
 
 The command above will generate the order model, but I’m taking advantage of the `belongs_to` column type to create the corresponding foreign key for the order to belong to a user. It also adds the `belongs_to` association into the order model. Let’s migrate the database.
@@ -166,7 +166,7 @@ $ git add . && git commit -m "Associates products and orders with a placements m
 ----
 
 
-== Expose the user model
+== Expose the order model
 
 It is now time to prepare the order controller to expose the right orders. If you remember the previous chapters where https://github.com/jsonapi-serializer/jsonapi-serializer[jsonapi-serializer] was used, you should remember that it was straightforward.