Fix error when updating checks via Pingdom API.

[gfokkema]

Apparently pingdom checks now output additional params lastdownstart
and lastdownend which the api is unable to handle as arguments.

Solves the following error:

Traceback (most recent call last):
...
  File "/home/gerloffokkema/.local/lib/python3.8/site-packages/pypingdom/client.py", line 81, in update_check
    self.api.send(method='put', resource='checks', resource_id=check._id, data=data)
  File "/home/gerloffokkema/.local/lib/python3.8/site-packages/pypingdom/api.py", line 48, in send
    raise ApiError(response)
pypingdom.api.ApiError: pingdom.ApiError: HTTP `400 - Bad Request` returned with message, "Invalid parameter: lastdownend."

[lawrencekoenig]

The Update you have created looks like the PR has failed due to a log failure. Can we have this retriggered?