Make cache max-age durations self-explanatory

railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt

@@ -18,7 +18,7 @@ Rails.application.configure do
 
     config.cache_store = :memory_store
     config.public_file_server.headers = {
-      'Cache-Control' => 'public, max-age=172800'
+      'Cache-Control' => "public, max-age=#{2.days.seconds.to_i}"
     }
   else
     config.action_controller.perform_caching = false

railties/lib/rails/generators/rails/app/templates/config/environments/test.rb.tt

@@ -15,7 +15,7 @@ Rails.application.configure do
   # Configure public file server for tests with Cache-Control for performance.
   config.public_file_server.enabled = true
   config.public_file_server.headers = {
-    'Cache-Control' => 'public, max-age=3600'
+    'Cache-Control' => "public, max-age=#{1.hour.seconds.to_i}"
   }
 
   # Show full error reports and disable caching.