Traceback: exceptions.AttributeError: Deferred instance has no attribute 'register'

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Updated my web server to master since #150 isn't in a release yet and now automat doesn't work with an old enough version of txacme that my pin broke, and now I'm getting this traceback:

2020-02-24T02:54:08+0000 [-] Unhandled Error
	Traceback (most recent call last):
	  File "/code/env/site-packages/txacme/service.py", line 282, in startService
	    self._timer_service.startService()
	  File "/code/env/site-packages/twisted/application/internet.py", line 275, in startService
	    self._loopFinished = self._loop.start(self.step, now=True)
	  File "/code/env/site-packages/twisted/internet/task.py", line 194, in start
	    self()
	  File "/code/env/site-packages/twisted/internet/task.py", line 239, in __call__
	    d = defer.maybeDeferred(self.f, *self.a, **self.kw)
	--- <exception caught here> ---
	  File "/code/env/site-packages/twisted/internet/defer.py", line 151, in maybeDeferred
	    result = f(*args, **kw)
	  File "/code/env/site-packages/txacme/service.py", line 143, in _check_certs
	    self._ensure_registered()
	  File "/code/env/site-packages/txacme/service.py", line 240, in _ensure_registered
	    return self._register()
	  File "/code/env/site-packages/txacme/service.py", line 251, in _register
	    self._client.register(regr)
	exceptions.AttributeError: Deferred instance has no attribute 'register'