Only try datetime_as_string on datetime kinded numpy arrays

Author: jonmmease

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

@@ -186,7 +186,7 @@ def encode_as_numpy(obj):
 
         if obj is numpy.ma.core.masked:
             return float("nan")
-        elif isinstance(obj, numpy.ndarray):
+        elif isinstance(obj, numpy.ndarray) and obj.dtype.kind == "M":
             try:
                 return numpy.datetime_as_string(obj).tolist()
             except TypeError: