- Previously this only included the formula name.
- But, for example in tests, we have "#{bin}/ansible-test",
  not just "#{bin}/ansible". So handle that too.
- I decided to make the error message better by extracting the
  binary name from the interpolation, but I'm not sure it was worth it.

```
$ brew audit --strict ansible
ansible
  * line 580, col 29: Use `bin/"ansible-test"` instead of `"#{bin}/ansible-test"`
Error: 1 problem in 1 formula detected.
```

- I couldn't get
  https://docs.rubocop.org/rubocop-ast/node_pattern.html#param_name-for-named-parameters
  to work like it said it should (bad syntax in the node_matcher, apart
  from with `bin = false` which RuboCop complained about boolean args not
  being named), so here's a workaround.