calling `make` or `make!` on an association does not set the new object's association to the calling object

This is easier to demonstrate than describe. I'm not sure if this is a feature or bug, but it works correctly in Machinist 1.

User has_many :posts
Post belongs_to :user

```
Post.blueprint do
  user
end

@user = User.make!

@new_post = @user.posts.make!

@new_post.user_id == @user.id # false in v. 2, true in v. 1
```
