heroku app/vendor/bundle shows wrong version of ruby - ruby-on-rails

Question

I'm am getting an error in production that doesn't occur in development. It appears in the stack trace that the gem is using the wrong version of ruby (2.1.0), but I have specified 2.1.3 in my gemfile and followed the heroku troubleshooting on ruby versions. Based on other stackoverflow information the ruby version makes a difference here. Anyone know how to update app/vendor/bundle to the latest?
This is my error which is occurring in a Resque worker...
undefined method `name' for nil:NilClass
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:72:in `block in initialize'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:74:in `yield'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:74:in `block in initialize'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:74:in `yield'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:74:in `block in initialize'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:74:in `yield'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:74:in `block in initialize'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:150:in `yield'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:150:in `accept'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych/visitors/yaml_tree.rb:114:in `push'
/app/vendor/bundle/ruby/2.1.0/gems/psych-2.0.6/lib/psych.rb:409:in `dump'
...snip...
This is my ruby version...
heroku run "ruby --version"
ruby 2.1.3p242 (2014-09-19 revision 47630) [x86_64-linux]
This is what's in /app/vendor/bundle...
heroku run "ls /app/vendor/bundle/ruby"
2.1.0
This is my Gemfile ruby declaration....
source 'https://rubygems.org'
group :default do
# current stable (heroku needs this listed)
ruby '2.1.3'
gem 'rails', '4.1.1'
gem 'redis' # queue mechanism
gem 'resque', "~> 1.22.0", :require => "resque/server"
gem 'resque_mailer' # mailer queue
gem 'resque-scheduler' # job scheduler
# postgres and database
gem 'pg' # postgres
gem 'activerecord-import' # bulk sql insert
gem 'seed-fu', '~> 2.3' # db seed data
# APIs
gem 'bitly'
gem 'feedjira' # RSS feeds
gem 'fullcontact'
gem 'httparty'# rest api client
gem 'twilio-ruby' # SMS
gem 'twitter'
gem 'twitter-text' # convert twitter, links, hashtags and users
gem 'yahoo-finance', require: 'yahoo_finance'
# WEB....
# Use unicorn as the app server
gem 'unicorn'
# javascript
gem 'jquery-rails'
gem 'uglifier', '>= 1.3.0' # compressor for js assets
gem 'coffee-rails', '~> 4.0.0'
# UI/CSS
gem 'sass-rails', '~> 4.0.0'
gem 'bootstrap-sass'
gem 'jquery-ui-rails'
gem 'jqcloud-rails' # word cloud
gem 'footable-rails' # mobile responsive table
gem 'font-awesome-sass'# icons
gem 'highcharts-rails'
# rails
gem 'turbolinks'
gem 'simple_form'
# admin interface
gem 'rails_admin' # models admin interface
gem "psych", "~> 2.0.5" # needed for rails_admin
# user authentication
gem 'devise'
gem 'domp'
gem 'omniauth'
gem 'omniauth-twitter'
gem 'omniauth-stocktwits', :git => 'https://github.com/jesseyoungmann/omniauth-stocktwits.git'
# app support
gem 'bcrypt', '~> 3.1.2' # for active model secure password
gem 'kaminari', :git => 'https://github.com/musicglue/kaminari.git' # pagination
end
# docs
group :doc do
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', require: false
end
# test
group :test do
gem "capybara"
gem 'factory_girl_rails'
gem 'faker'
gem 'rspec-rails'
gem 'selenium-webdriver'
gem 'simplecov', :require => false
gem 'vcr', '~> 2.8.0'
gem 'webmock', '~> 1.15.0'
end
# development
group :development do
gem 'foreigner', '~> 1.6.1' # foreign key generator
gem 'rails_layout'
# profilers
gem 'rack-mini-profiler'
gem 'ruby-prof'
end
group :production do
gem 'newrelic_rpm'
gem 'rails_12factor' # heroku
end
Thanks!

Answer 1

A possible solution is to create a .ruby-version file in the root of your application and simply put 2.1.3 in it, than your app will always use that version in production and development. I had similar issues in the past and this did the trick for me.

Answer 2

Duplicate of this:
Why Do Heroku Stack Traces indicate Ruby 1.9.1 is in use?
Same answer as this:
Why are we installing Ruby 1.9.2/1.9.3 gems into a 1.9.1 folder?