<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def prune_builds(self):
 """ Delete the builder cache Returns: (dict):
 A dictionary containing information about the operation's result. The ``SpaceReclaimed`` key indicates the amount of bytes of disk space reclaimed. Raises: :py:class:`docker.errors.APIError` If the server returns an error. """

        url = self._url("/build/prune")
        return self._result(self._post(url), True)