np.minimum.accumulate(da) doesn't work

Code Sample, a copy-pastable example if possible

In [1]: import numpy as np

In [2]: import xarray as xr

In [3]: np.minimum.accumulate(np.array([3,2,4,1]))
Out[3]: array([3, 2, 2, 1], dtype=int32)

In [4]: np.minimum.accumulate(xr.DataArray([3,2,4,1]))
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
<ipython-input-7-7205433fb365> in <module>()
----> 1 np.minimum.accumulate(xr.DataArray([3,2,4,1]))
~\Anaconda3\lib\site-packages\xarray\core\arithmetic.py in __array_ufunc__(self, ufunc, method, *inputs, **kwargs)
     49                 'alternative, consider explicitly converting xarray objects '
     50                 'to NumPy arrays (e.g., with `.values`).'
---> 51                 .format(method, ufunc))
     52
     53         if any(isinstance(o, SupportsArithmetic) for o in out):
NotImplementedError: accumulate method for ufunc <ufunc 'minimum'> is not implemented on xarray objects, which currently only support the __call__ method. As an alternative, consider explicitly converting xarray objects to NumPy arrays (e.g., with `.values`).

Problem description

I would expect this to work, like xr.apply_ufunc(np.minimum.accumulate, xr.DataArray([3,2,4,1])):

Expected Output

 Out[4]:  <xarray.DataArray (dim_0: 4)>
          array([3, 2, 2, 1])
          Dimensions without coordinates: dim_0

Output of xr.show_versions()

Originally posted posted to https://groups.google.com/forum/#!topic/xarray/LiwxrJcJBwY.

Start with xarray/core/arithmetic.py, where the traceback shows array_ufunc rejecting the accumulate method. Reproduce the example with np.minimum.accumulate on a DataArray and verify that the operation returns a DataArray with the expected values and dimensions.