CtkCanvas.coords add return values (fixes #1419)

[DerSchinken]

CtkCanvas.coords was missing the return values (the coords), with this fix the method will always return the values from the call to the parents method (super().coord). Fixing #1419

[MrHarcombe]

This is affecting me, too - have ended up making a similar change, locally, so I can carry on using this otherwise excellent library 👍