Failure result not returned

When a script in "rss" returns failure, the return code is not passed out of rss. This makes it hard to spot problems among large outputs and allows CI/CD pipelines to proceed despite errors.

Simple test:

package.json
```json
{
  "rss": {
    "false: "false"
  }
}
```

CLI:
```
$ npx rss false
$ echo $?
```

**Expected**: 1  (error response)
**Observed**: 0  (no error)
