issue exporting config

### **This is autogenerated. Please review and update as needed.**

## Describe the bug
My initial attempt to export my cluster config, I simply ran: az kube export --
**Command Name**
`az kube export
Extension Name: azure-kube-cli. Version: 0.0.1.`

**Errors:**
```
Invalid kube-config file. No configuration found.
Traceback (most recent call last):
python3.6/site-packages/knack/cli.py, ln 215, in invoke
cmd_result = self.invocation.execute(args)
cli/core/commands/__init__.py, ln 654, in execute
raise ex
cli/core/commands/__init__.py, ln 718, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
...
azure-kube-cli/kubernetes/config/kube_config.py, ln 739, in load_kube_config
persist_config=persist_config)
azure-kube-cli/kubernetes/config/kube_config.py, ln 701, in _get_kube_config_loader_for_yaml_file
'Invalid kube-config file. '
kubernetes.config.config_exception.ConfigException: Invalid kube-config file. No configuration found.
```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- _Put any pre-requisite steps here..._
- `az kube export --kubeconfig=./myconfig--verbose`

## Expected Behavior

## Environment Summary
```
Linux-4.15.0-1092-azure-x86_64-with-debian-stretch-sid (Cloud Shell)
Python 3.6.10
Installer: DEB

azure-cli 2.11.1

Extensions:
azure-kube-cli 0.0.1
ai-examples 0.2.3

```
## Additional Context