ActiveAdmin: Allow for both singular and plural model names (#776)

This is an addition to this PR: #692
I've seen it's been stale for a while and it's rather simple fix.

I noticed my ActiveAdmin resources are not being annotated.
I know ActiveAdmin uses plural model names, but, as far as I remember, they used to use singular model names in the past.

We can see some "evidence" of that here: https://activeadmin.info/2-resource-customization.html#customizing-parent-menu-items
Probably in other places as well.

In order to keep the gem working as expected for singular ActiveAdmin resources, I suggest we annotate both singular and plural model names.

I just tested this out in a project of mine where I renamed one file to be in singular form and left the other files in plural form.
It worked like a charm. :)

Author: vfonic

lib/annotate/annotate_models/file_patterns.rb

@@ -59,7 +59,10 @@ def generate(root_directory, pattern_type, options)
         when 'controller'
           [File.join(root_directory, CONTROLLER_DIR, '%PLURALIZED_MODEL_NAME%_controller.rb')]
         when 'admin'
-          [File.join(root_directory, ACTIVEADMIN_DIR, '%MODEL_NAME%.rb')]
+          [
+            File.join(root_directory, ACTIVEADMIN_DIR, '%MODEL_NAME%.rb'),
+            File.join(root_directory, ACTIVEADMIN_DIR, '%PLURALIZED_MODEL_NAME%.rb')
+          ]
         when 'helper'
           [File.join(root_directory, HELPER_DIR, '%PLURALIZED_MODEL_NAME%_helper.rb')]
         else

spec/lib/annotate/annotate_models/file_patterns_spec.rb

@@ -119,10 +119,8 @@
     context 'when pattern_type is "admin"' do
       let(:pattern_type) { 'admin' }
 
-      it 'returns patterns of admin files' do
-        is_expected.to eq([
-          '/root/app/admin/%MODEL_NAME%.rb'
-        ])
+      it 'returns both singular and pluralized model names' do
+        is_expected.to eq(['/root/app/admin/%MODEL_NAME%.rb', '/root/app/admin/%PLURALIZED_MODEL_NAME%.rb'])
       end
     end