Docs: Update bag.rst (#4199)
Docs: Update bag.rst (#4199)

This PR updates `bag.rst` with a single fix: split *Dask.Bag* to *Dask Bag*.
dask/dask,dask/dask,blaze/dask,jcrist/dask,mrocklin/dask,ContinuumIO/dask,jcrist/dask,ContinuumIO/dask,jakirkham/dask,mrocklin/dask,blaze/dask,jakirkham/dask