Support latest pandas

[dhirschfeld]

All the changes in the recent pandas release has broken compatibility - e.g.

..\_t_env\lib\site-packages\pandas_msgpack\packers.py:58: in <module>
    from pandas.sparse.api import SparseSeries, SparseDataFrame

Should now be from pandas.core.sparse.api import ...?

[jreback]

yeah haven't updated this.