fix bug in textblock
fix bug in textblock

jakirkham/dask,ContinuumIO/dask,dask/dask,pombredanne/dask,cowlicks/dask,dask/dask,blaze/dask,mraspaud/dask,blaze/dask,gameduell/dask,vikhyat/dask,ContinuumIO/dask,mikegraham/dask,jakirkham/dask,chrisbarber/dask,mrocklin/dask,mraspaud/dask,jcrist/dask,jcrist/dask,pombredanne/dask,vikhyat/dask,cpcloud/dask,mrocklin/dask