Adjusting generator template example to match anycable-go cli signature

[germs12]

Found a typo while working through the ActionCable Getting Started Docs (https://docs.anycable.io/rails/getting_started)

Also just returned from RailsConf and I'm eager to give back to the community. Here's my first!

Checklist

• [ ] I've added tests for this change
• [ ] I've added a Changelog entry
• [x] I've updated documentation

[palkan]

Thanks!