Re-add the `complete` extra (#6257)
Re-add the `complete` extra (#6257)

Mistakenly removed when making pyyaml a required dependency.
dask/dask,blaze/dask,ContinuumIO/dask,jakirkham/dask,jakirkham/dask,mrocklin/dask,blaze/dask,mrocklin/dask,dask/dask,ContinuumIO/dask