Ensuring that Rails loads up for our specs

Prior to this change, when I would run `rspec` from the command line,
I would get the following exception:
    spec/models/user_spec.rb:3:in `<top (required)>':
      uninitialized constant User (NameError)

What was happening is that rspec without the spec_helper changes was
unable to find where the User class was defined.

By adding these lines Rails now successfully boots.
Generating devise user

The following commands were run:
$ rails generate devise User