Get user by id error: Requested resource is not available in current API version

[eapermyakov]

Python: 3.6.4
Python-intercom: 3.1.0

DEBUG:intercom.request:Sending GET request to: https://api.intercom.io/users
DEBUG:intercom.request:  headers: {'User-Agent': 'python-intercom/3.1.0', 'AcceptEncoding': 'gzip, deflate', 'Accept': 'application/json'}
DEBUG:intercom.request:  params: {'user_id': 123456789}
DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): api.intercom.io
DEBUG:requests.packages.urllib3.connectionpool:https://api.intercom.io:443 "GET /users?user_id=123456789 HTTP/1.1" 400 None
DEBUG:intercom.request:Response received from https://api.intercom.io/users
DEBUG:intercom.request:  encoding=utf-8 status:400
DEBUG:intercom.request:  content:
b'{"type":"error.list","request_id":"0008********00","errors":[{"code":"intercom_version_invalid","message":"Requested resource is not available in current API version"}]}'

[pbadeer]

Related to #221