az devops invoke does not resolve the route correctly in some cases - ends up hitting the wrong endpoint

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

## Describe the bug

**Command Name**
`az devops invoke
Extension Name: azure-devops. Version: 0.15.0.`

**Errors:**
```
'type'
Traceback (most recent call last):
pip-install-6e754znd\knack\knack\cli.py, ln 206, in invoke
cli\core\commands\__init__.py, ln 603, in execute
cli\core\commands\__init__.py, ln 661, in _run_jobs_serially
cli\core\commands\__init__.py, ln 652, in _run_job
azext_devops\dev\common\exception_handler.py, ln 31, in azure_devops_exception_handler
reraise(*sys.exc_info())
Temp\pip-install-6e754znd\six\six.py, ln 693, in reraise
cli\core\commands\__init__.py, ln 631, in _run_job
...
azure-devops\azext_devops\devops_sdk\client.py, ln 63, in _send
query_parameters=query_parameters)
azure-devops\azext_devops\devops_sdk\client.py, ln 116, in _create_request_message
url = self._client.format_url(route_template, **route_values)
pip-install-6e754znd\msrest\msrest\service_client.py, ln 151, in format_url
KeyError: 'type'
```

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

- `az devops invoke --area wit --resource workitems --route-parameters project= id=`

replace and with valid values for a project in Azure DevOps and a workitem id

## Expected Behavior

Return workitem details. Should work like the rest api:
https://docs.microsoft.com/en-us/rest/api/azure/devops/wit/work%20items/get%20work%20item?view=azure-devops-rest-5.1#workitemexpand

## Environment Summary
```
Windows-10-10.0.18362-SP0
Python 3.6.6
Shell: powershell.exe

azure-cli 2.0.74 *

Extensions:
azure-devops 0.15.0

```
## Additional Context