Correct test_textblock test.
Correct test_textblock test.

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