ArgumentError in actionpack-2.3.18/lib/action_controller/session/cookie_store.rb

[LucasCioffi]

Hi all, I'm seeing this error when deploying to Heroku:

2017-07-27T20:31:51.485945+00:00 app[web.1]: /app/vendor/bundle/ruby/1.9.1/gems/actionpack-
2.3.18/lib/action_controller/session/cookie_store.rb:194:in `ensure_secret_secure': A secret is 
required to generate an integrity hash for cookie session data. Use config.action_controller.session 
= { :key => "_myapp_session", :secret => "some secret phrase of at least 30 characters" } in 
config/environment.rb (ArgumentError)

But it seems like I have set up config/environment.rb correctly:

# Be sure to restart your server when you modify this file
Encoding.default_external = Encoding.default_internal = Encoding::UTF_8 if defined? Encoding

# Specifies gem version of Rails to use when vendor/rails is not present
RAILS_GEM_VERSION = '2.3.18' unless defined? RAILS_GEM_VERSION

# Bootstrap the Rails environment, frameworks, and default configuration
require File.join(File.dirname(__FILE__), 'boot')

Rails::Initializer.run do |config|
  # Settings in config/environments/* take precedence over those specified here.

  config.active_record.default_timezone = :utc

  config.action_mailer.delivery_method = :smtp
  config.action_controller.session = { :key => "_myapp_session", :secret => "somesecretphraseofatleast30characters" }
end
ActionController::Base.cache_store = :file_store, "#{Rails.root}/tmp/cache"

Any suggestions? Thank you!