hclsimple cannot parse subscribe_event_types

Input policy

```
# comment
# comment

path "some/path/*" {
  capabilities = ["read", "list", "subscribe"]
  subscribe_event_types = ["*"]
}
```

Result
```
policy.hcl:6,3-24: Unsupported argument; An argument named "subscribe_event_types" is not expected here.
```
