{{ index }} not working

[TonyGiorgio]

I see this PR: https://github.com/fcsonline/drill/issues/89

But when I do this very simple repro:

concurrency: 1
iterations: 1

plan:
  - name: Initial assignment for version {{ index }}
    assert:
      key: index
      value: 0

I get:

Initial assignment for version {{ index }} index=0?
thread 'main' panicked at /home/dev/.cargo/registry/src/index.crates.io-6f17d22bba15001f/drill-0.8.2/src/interpolator.rs:44:11:
Unknown 'index' variable!