Prevent silent fail

Hi!,

We are using this command in our CI/CD pipeline:

```
fetch --repo="https://github.com/..." --tag="1.0.9" --github-oauth-token="****" --release-asset="example-v1.0.9.zip" tmp-path
```

Yesterday this command fails because of a GitHub authorization error, however, it only logs the error instead of exiting with non-zero code this causes the pipeline to continue then exist on another step that depends on what has been downloaded by `fetch`.

Please we need an option to exit on error.