Variable spelling fix

[bobhenkel]

High-level description of the change.

• Update doc spelling of worker_preemeptible to match the variable value(worker_preemptible) in one location in the document.

Testing

Ran terraform plan after trying variable worker_preemeptible and terraform failed asking if I meant worker_preemptible. I updated spelling in my tf to worker_preemptibleand did terraform plan and all was good.

rel: issue number (if applicable)

[dghubble]

Thanks!