undefined method `cattr_accessor' with this gem

[schneems]

I'm trying to use this gem in a non-rails project and when I do I get this error:

Gem Load Error is: undefined method `cattr_accessor' for Librato::Sidekiq::Middleware:Class
Did you mean?  attr_accessor
Backtrace for gem load error is:
/app/vendor/bundle/ruby/2.5.0/gems/librato-sidekiq-0.1.2/lib/librato-sidekiq/middleware.rb:4:in `<class:Middleware>'
/app/vendor/bundle/ruby/2.5.0/gems/librato-sidekiq-0.1.2/lib/librato-sidekiq/middleware.rb:3:in `<module:Sidekiq>'
/app/vendor/bundle/ruby/2.5.0/gems/librato-sidekiq-0.1.2/lib/librato-sidekiq/middleware.rb:2:in `<module:Librato>'
/app/vendor/bundle/ruby/2.5.0/gems/librato-sidekiq-0.1.2/lib/librato-sidekiq/middleware.rb:1:in `<top (required)>'
/app/vendor/bundle/ruby/2.5.0/gems/librato-sidekiq-0.1.2/lib/librato-sidekiq.rb:1:in `require'
/app/vendor/bundle/ruby/2.5.0/gems/librato-sidekiq-0.1.2/lib/librato-sidekiq.rb:1:in `<top (required)>'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler/runtime.rb:82:in `require'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler/runtime.rb:82:in `block (2 levels) in require'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler/runtime.rb:77:in `each'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler/runtime.rb:77:in `block in require'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler/runtime.rb:66:in `each'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler/runtime.rb:66:in `require'
/app/vendor/bundle/ruby/2.5.0/gems/bundler-1.15.2/lib/bundler.rb:108:in `require'

It looks like maybe you're expecting cattr_accessor to be available from some other gem perhaps active support? You need to find it and add it to the gemspec.