add destroy language test

spec/acceptance/languages_spec.rb

@@ -48,8 +48,19 @@ resource 'Languages' do
       do_request
       expect(status).to eq(201)
     end
+  end
+
+  delete '/v1/languages/:id' do
+    include_context "authenticate_user"
+
+    parameter :id, 'The id of the language'
 
+    let(:id) { languages.first.id }
 
+    example 'Destroying a language' do
+      do_request
+      expect(status).to eq(200)
+    end
   end