bump version to 0.20.1
bump version to 0.20.1

blaze/dask,dask/dask,jakirkham/dask,blaze/dask,ContinuumIO/dask,ContinuumIO/dask,dask/dask,jcrist/dask,mrocklin/dask,jcrist/dask,mrocklin/dask,jakirkham/dask