[ci skip] Spell out the full variable in generated code.

railties/lib/rails/generators/rails/app/templates/config/initializers/content_security_policy.rb.tt

@@ -17,7 +17,7 @@
 # end
 
 # If you are using UJS then enable automatic nonce generation
-# Rails.application.config.content_security_policy_nonce_generator = ->(req) { SecureRandom.base64(16) }
+# Rails.application.config.content_security_policy_nonce_generator = -> request { SecureRandom.base64(16) }
 
 # Report CSP violations to a specified URI
 # For further information see the following documentation: