Repository: auth0/auth0-python

Issue:
rules_config.unset does not work
### Description

`rules_config.unset` does not work. It returns a 404 for a known existing key. I believe this is because the `key` param is being passed to the auth0 api as a query param when it should be a path param according to the docs.

https://auth0.com/docs/api/management/v2#!/Rules_Configs/delete_rules_configs_by_key

### Prerequisites

- [x] I have checked the [README documentation](https://github.com/auth0/auth0-python/blob/master/README.rst).
- [x] I have checked the [Auth0 Community](https://community.auth0.com/) for related posts.
- [x] I have checked for related or duplicate [Issues](https://github.com/auth0/auth0-python/issues) and [PRs](https://github.com/auth0/auth0-python/pulls).
- [x] I have read the [Auth0 general contribution guidelines](https://github.com/auth0/open-source-template/blob/master/GENERAL-CONTRIBUTING.md).
- [x] I have read the [Auth0 Code of Conduct](https://github.com/auth0/open-source-template/blob/master/CODE-OF-CONDUCT.md).
- [x] I am reporting this to the correct repository.

### Environment

- auth0-python 3.7.2
- python 3.7.0

### Reproduction
Code Sample:

```
from auth0.v3.authentication import GetToken
from auth0.v3.management import Auth0
get_token = GetToken('xxx.auth0.com')
mgmt_api_token = get_token.client_credentials('xxx',
                                            'xxx', 'https://{}/api/v2/'.format('xxx.auth0.com'))
auth0 = Auth0('xxx.auth0.com', mgmt_api_token['access_token'])
key_name = 'FOO'
auth0.rules_configs.set(key_name, 'BAR')
rules_configs = auth0.rules_configs.all()
print(rules_configs)
auth0.rules_configs.unset(key_name)
```

Output:

```
[{'key': 'FOO'}]
Traceback (most recent call last):
  File "<input>", line 13, in <module>
  File "/Users/jhunken/.pyenv/versions/securityPlatform-3.5.3/lib/python3.5/site-packages/auth0/v3/management/rules_configs.py", line 45, in unset
    return self.client.delete(self._url(), params=params)
  File "/Users/jhunken/.pyenv/versions/securityPlatform-3.5.3/lib/python3.5/site-packages/auth0/v3/management/rest.py", line 75, in delete
    return self._process_response(response)
  File "/Users/jhunken/.pyenv/versions/securityPlatform-3.5.3/lib/python3.5/site-packages/auth0/v3/management/rest.py", line 78, in _process_response
    return self._parse(response).content()
  File "/Users/jhunken/.pyenv/versions/securityPlatform-3.5.3/lib/python3.5/site-packages/auth0/v3/management/rest.py", line 98, in content
    message=self._error_message())
auth0.v3.exceptions.Auth0Error: 404: Not Found
```


Comments:

Patch:
diff --git a/auth0/v3/management/rules_configs.py b/auth0/v3/management/rules_configs.py
index cfde7b0..686f101 100644
--- a/auth0/v3/management/rules_configs.py
+++ b/auth0/v3/management/rules_configs.py
@@ -39,10 +39,7 @@ class RulesConfigs(object):
 
         See: https://auth0.com/docs/api/management/v2#!/Rules_Configs/delete_rules_configs_by_key
         """
-        params = {
-            'key': key
-        }
-        return self.client.delete(self._url(), params=params)
+        return self.client.delete(self._url(key))
 
     def set(self, key, value):
         """Sets the rules config for a given key.


Test patch:
diff --git a/auth0/v3/test/management/test_rules_configs.py b/auth0/v3/test/management/test_rules_configs.py
index 68ee018..d3c41e5 100644
--- a/auth0/v3/test/management/test_rules_configs.py
+++ b/auth0/v3/test/management/test_rules_configs.py
@@ -25,7 +25,7 @@ class TestRules(unittest.TestCase):
         c.unset('an-id')
 
         mock_instance.delete.assert_called_with(
-            'https://domain/api/v2/rules-configs', params={'key': 'an-id'}
+            'https://domain/api/v2/rules-configs/an-id'
         )
 
     @mock.patch('auth0.v3.management.rules_configs.RestClient')