When API Key is recycled and 403s are returned, the library returns a KeyError #11

 File "/usr/local/lib/python3.8/site-packages/activecampaign/contacts.py", line 16, in create_a_contact
 return self.client._post("/contacts", json=data)
 File "/usr/local/lib/python3.8/site-packages/activecampaign/client.py", line 37, in _post
 return self._request('POST', endpoint, **kwargs)
 File "/usr/local/lib/python3.8/site-packages/activecampaign/client.py", line 54, in _request
 return self._parse(requests.request(method, self.BASE_URL + endpoint, headers=_headers, **kwargs))
 File "/usr/local/lib/python3.8/site-packages/activecampaign/client.py", line 57, in _parse
 if 'application/json' in response.headers['Content-Type']:
 File "/usr/local/lib/python3.8/site-packages/requests/structures.py", line 54, in __getitem__
 return self._store[key.lower()][1]
KeyError: 'content-type'