ajv-cli dies when evaluating yaml with duplicate object keys

When running on yml with duplicate object keys, ajv fails and errors out with the following error. Let me know if this is something I'm missing on my side?

Command
```
ajv validate -d "definitions/v3/*.yml" -s "definitions/v3/schema.json" --verbose
```

Error:
```
error: Invalid left-hand side expression in prefix operation
```

Example Yaml
```
---
id: example
name: Example

caps:
date: pass
date: other
```

Version: 5.0.0 (installed via npm)
Scemas: Tested with a draft07 and draft2020