Fix activeadmin filename issue

[murugan-r]

Fixes #16 .

[arjunvenkat]

It looks like this fix actually makes the generated model filenames and classnames plural instead.

For example,

rails g draft:resource Actor name

Will generate a model file called actors.rb:

class Actors < ApplicationRecord
end

and the same goes for the ActiveAdmin file of actors.rb

[arjunvenkat]

The above comment is being addressed by: Issue#28