Rails/Rspec: uninitialized constant Rails (NameError)

Rails/Rspec: uninitialized constant Rails (NameError)

When I run bundle exec rake spec I keep running into this error:
uninitialized constant Rails (NameError)
Here is my gemfile:
group :development do
gem 'guard-rspec'
gem 'guard-spork'
end
group :development, :test do
gem "debugger-ruby_core_source", "~> 1.2.2"
gem 'debugger'
gem 'faker'
gem 'rspec-rails'
gem 'factory_girl_rails'
gem 'spork-rails', "~> 3.2"
gem "database_cleaner", "~> 0.9"
end
group :test do
gem 'capybara'
gem 'guard-rspec'
gem 'launchy'
gem "shoulda-matchers", "~> 2.0"
gem "selenium-webdriver"
gem "rspec-sidekiq"
end
I can't figure out why this is happening...