use double-quotes as suggested by black

Author: bmaranville

packages/python/plotly/plotly/basedatatypes.py

@@ -4777,7 +4777,7 @@ def __contains__(self, prop):
                 else:
                     return False
             else:
-                if hasattr(obj, '_valid_props') and p in obj._valid_props:
+                if hasattr(obj, "_valid_props") and p in obj._valid_props:
                     obj = obj[p]
                 else:
                     return False