We should be able to filter by symbols

spec/app_spec.rb

@@ -17,4 +17,10 @@ describe 'the application' do
     get '/latest?base=USD'
     json['base'].must_equal 'USD'
   end
+
+  it 'filters symbols' do
+    skip 'enterprise feature'
+    get '/latest?symbols=USD'
+    json['rates'].keys.must_equal %w(USD)
+  end
 end