Pre 1.0 pandas compatibilty

Author: jonmmease

Diff for: packages/python/plotly/_plotly_utils/basevalidators.py

@@ -104,7 +104,7 @@ def copy_to_readonly_numpy_array(v, kind=None, force_numeric=False):
                 # DatetimeIndex
                 v = v.to_pydatetime()
     elif pd and isinstance(v, pd.DataFrame) and len(set(v.dtypes)) == 1:
-        dtype = v.dtypes[0]
+        dtype = v.dtypes.tolist()[0]
         if dtype.kind in numeric_kinds:
             v = v.values
         elif dtype.kind == "M":