Revert "Temporarly pin sphinx version to 3.3.1 (#7002)" (#7014)
Revert "Temporarly pin sphinx version to 3.3.1 (#7002)" (#7014)

This reverts commit 4a7a2438219c4ee493434042e50f4cdb67b6ec9f.
jakirkham/dask,blaze/dask,dask/dask,dask/dask,jakirkham/dask,blaze/dask