Fix pandas BaseIndexer import (#377)

Author: charlesbluca

dask_sql/physical/rel/logical/window.py

@@ -6,7 +6,7 @@
 import dask.dataframe as dd
 import numpy as np
 import pandas as pd
-from pandas.core.window.indexers import BaseIndexer
+from pandas.api.indexers import BaseIndexer
 
 from dask_sql.datacontainer import ColumnContainer, DataContainer
 from dask_sql.java import org