tkwidgets: fix missing sys import from Valuator.py

[skip ci]

direct/src/tkwidgets/Valuator.py

@@ -8,6 +8,7 @@ from . import WidgetPropertiesDialog
 import Pmw
 from direct.directtools.DirectUtil import getTkColorString
 from panda3d.core import Vec4
+import sys
 
 if sys.version_info >= (3, 0):
     from tkinter.colorchooser import askcolor