fix link typo in single-distributed docs
fix link typo in single-distributed docs

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