[ci skip] use true as value rather than symbol

guides/source/association_basics.md

@@ -933,7 +933,7 @@ Passing `true` to the `:polymorphic` option indicates that this is a polymorphic
 
 ##### `:touch`
 
-If you set the `:touch` option to `:true`, then the `updated_at` or `updated_on` timestamp on the associated object will be set to the current time whenever this object is saved or destroyed:
+If you set the `:touch` option to `true`, then the `updated_at` or `updated_on` timestamp on the associated object will be set to the current time whenever this object is saved or destroyed:
 
 ```ruby
 class Order < ActiveRecord::Base