docs-bug(stepper): stepper errors not working in documentation

[troywweber7]

Documentation Feedback

The following example is not showing the messages in the example code: https://material.angular.io/components/stepper/overview#error-state

This could be a general bug as I can't get errors to show in my own project either.

Affected documentation page: https://material.angular.io/components/stepper/overview#error-state

[crisbeto]

The example is mostly set up correctly, the problem is that the stepper is marked as linear which means that you can't move off of the current step in order to see the error. I've submitted a PR to make it non-linear and expand the example description.