Shorten secret_token

Since we don't care what it is, we can generate a dumb one in just a few
characters.

config.ru

@@ -7,7 +7,7 @@ require 'uri'
 class TheSmallestRailsApp < Rails::Application
   routes.append { root to: 'hello#world' }
 
-  config.secret_token = 'not so secret but long enough to please rails'
+  config.secret_token = 'a'*30
   config.logger       = Logger.new STDOUT
 end