ActionController::ParameterMissing in users#update

When editing a user from `Submittor` to `Crew`, I got this

```
An ActionController::ParameterMissing occurred in users#update:

  param is missing or the value is empty: user
  app/controllers/users_controller.rb:74:in `user_params'
```

assumingly because `params[:user].delete(:role)` left `params[:user]` empty 