reduce scale of concurrency test
reduce scale of concurrency test

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