use config.update_defaults in dask.array (#3532)
use config.update_defaults in dask.array (#3532)

This records the defaults so that they survive refresh events
jcrist/dask,mrocklin/dask,mrocklin/dask,dask/dask,blaze/dask,dask/dask,jcrist/dask,jakirkham/dask,jakirkham/dask,ContinuumIO/dask,ContinuumIO/dask,blaze/dask