Fix a minor typo in the changelog (#2898)
Fix a minor typo in the changelog (#2898)

`_unique_interlal` should be `_unique_internal`.

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blaze/dask,blaze/dask,mrocklin/dask,ContinuumIO/dask,jakirkham/dask,jcrist/dask,dask/dask,jakirkham/dask,dask/dask,jcrist/dask,mrocklin/dask,ContinuumIO/dask