Check If Record Has DeletedAt Column

## Context
Previously, when model with has_many association without `deleted_at` column will
raise "undefined method deleted_at=" error.

With this change, it will revert to original destroy behavior when the record
does not have `deleted_at` column.

lib/permanent_records.rb

@@ -215,7 +215,7 @@ def permanently_delete_records(dependent_records)
           record = klass.unscoped.where(klass.primary_key => id).first
           next unless record
 
-          record.deleted_at = nil
+          record.deleted_at = nil if record.respond_to?(:deleted_at)
           record.destroy(:force)
         end
       end

spec/permanent_records_spec.rb

@@ -10,7 +10,8 @@
   let!(:location)   { hole.create_location                  }
   let!(:difficulty) { hole.create_difficulty                }
   let!(:comments)   { 2.times.map { hole.comments.create! } }
-  let!(:kitty)      { Kitty.create!                         }
+  let!(:bed)        { Bed.create!                           }
+  let!(:kitty)      { Kitty.create!(beds: [bed])               }
   let!(:meerkat)    { Meerkat.create!(holes: [hole])        }
 
   describe '#destroy' do
@@ -97,18 +98,6 @@
       end
     end
 
-    context 'when model has no deleted_at column' do
-      let(:record) { kitty }
-
-      it 'really removes the record' do
-        expect { subject }.to change { record.class.count }.by(-1)
-      end
-
-      it 'makes deleted? return true' do
-        expect(subject).to be_deleted
-      end
-    end
-
     context 'with dependent records' do
       context 'that are permanent' do
         it '' do
@@ -202,6 +191,24 @@
         it 'removes them' do
           expect { subject }.to change { Mole.count }.by(-1)
         end
+
+        context 'with has many cardinality' do
+          context 'when model has no deleted_at column' do
+            let(:record) { kitty }
+
+            it 'really removes the record' do
+              expect { subject }.to change { record.class.count }.by(-1)
+            end
+
+            it 'really removes the associations' do
+              expect { subject }.to change { Bed.count }.by(-1)
+            end
+
+            it 'makes deleted? return true' do
+              expect(subject).to be_deleted
+            end
+          end
+        end
       end
 
       context 'as default scope' do
@@ -293,7 +300,7 @@
         end
 
         context 'that were deleted previously' do
-          before { muskrat.update_attributes! deleted_at: 2.minutes.ago }
+          before { muskrat.update_attribute :deleted_at, 2.minutes.ago }
           it 'does not restore' do
             expect { subject }.to_not change(muskrat, :deleted?)
           end

spec/support/bed.rb

@@ -0,0 +1,3 @@
+class Bed < ActiveRecord::Base
+  has_one :kitty
+end

spec/support/kitty.rb

@@ -1,2 +1,3 @@
 class Kitty < ActiveRecord::Base
+  has_and_belongs_to_many :beds, dependent: :destroy
 end

spec/support/schema.rb

@@ -13,8 +13,18 @@
     t.references :hole
   end
 
+  create_table :beds, force: true do |t|
+    t.column :name, :string
+  end
+
   create_table :kitties, force: true do |t|
     t.column :name, :string
+    t.references :bed
+  end
+
+  create_table :beds_kitties, force: true do |t|
+    t.references :kitty
+    t.references :bed
   end
 
   create_table :holes, force: true do |t|