Error if using dask_ml.preprocessing RobustScaler

I want to use RobustScaler and got following error:
```
Traceback (most recent call last):
File "", line 14, in
File "/home/magehex/anaconda3/envs/reinbo/lib/python3.7/site-packages/sklearn/base.py", line 556, in fit_transform
return self.fit(X, y, **fit_params).transform(X)
File "/home/magehex/anaconda3/envs/reinbo/lib/python3.7/site-packages/dask_ml/preprocessing/data.py", line 180, in fit
quantiles = [da.percentile(col, [q_min, 50.0, q_max]) for col in X.T]
File "/home/magehex/anaconda3/envs/reinbo/lib/python3.7/site-packages/dask_ml/preprocessing/data.py", line 180, in
quantiles = [da.percentile(col, [q_min, 50.0, q_max]) for col in X.T]
File "/home/magehex/anaconda3/envs/reinbo/lib/python3.7/site-packages/dask/array/percentile.py", line 133, in percentile
for i, key in enumerate(a.__dask_keys__())
AttributeError: 'numpy.ndarray' object has no attribute '__dask_keys__'
```

Code:
```
import numpy as np
from dask_ml.preprocessing import RobustScaler
import time
from sklearn.datasets.samples_generator import make_blobs

# generate 2d classification dataset
X, y = make_blobs(n_samples=100000, centers=2, n_features=380)

X_train = X.astype(np.float32)
y_train = y.astype(np.int32)

start = time.time()

RobustScaler().fit_transform(X_train,y_train)

end = time.time()
print(end - start)
```