add pandas to requirements-docs
add pandas to requirements-docs

ContinuumIO/dask,clarkfitzg/dask,jakirkham/dask,PhE/dask,wiso/dask,mrocklin/dask,freeman-lab/dask,clarkfitzg/dask,vikhyat/dask,ssanderson/dask,mrocklin/dask,chrisbarber/dask,jcrist/dask,vikhyat/dask,simudream/dask,pombredanne/dask,freeman-lab/dask,wiso/dask,ssanderson/dask,jcrist/dask,gameduell/dask,ContinuumIO/dask,dask/dask,PhE/dask,simudream/dask,mraspaud/dask,jayhetee/dask,cpcloud/dask,blaze/dask,pombredanne/dask,mraspaud/dask,jakirkham/dask,jayhetee/dask,mikegraham/dask,dask/dask,blaze/dask,cowlicks/dask