Logging Action Cable to STDOUT caused the development log to see double
messages like this:

```
Started GET "/" for ::1 at 2015-12-17 15:21:34 -0500
Started GET "/" for ::1 at 2015-12-17 15:21:34 -0500
Processing by Rails::WelcomeController#index as HTML
Processing by Rails::WelcomeController#index as HTML
Rendered /welcome/index.html.erb (0.0ms)
Rendered /welcome/index.html.erb (0.0ms)
Completed 200 OK in 3ms (Views: 1.3ms | ActiveRecord: 0.0ms)
Completed 200 OK in 3ms (Views: 1.3ms | ActiveRecord: 0.0ms)
```

Now that Action Cable is part of Rails it doesn't need it's own logger
and will log to STDOUT via the local dev server here:
https://github.com/rails/rails/blob/master/railties/lib/rails/commands/server.rb