The "currentField" property of the "k8sAutoscale" node does not populate the given field

Similar to #2251, but for the `k8sAutoscale` node. When given a TICKscript like so:

```
|k8sAutoscale()
.currentField('currentScale')
.namespace('prod')
.resourceName('my-deployment')
.kind('deployments')
.increaseCooldown(5m)
.decreaseCooldown(2m)
.replicas(lambda: "currentScale" + 1)
```

it yields the following error:
```
failed to evaluate the replicas expression: left value is invalid value type
```

Which suggests that the `currentScale` field is not being filled in.

This occurs on the `kapacitor:1.5.3-alpine` Docker image, but has not been tested in other environments.