generated labels are shifted to top left by 10 pixels

[cmosig]

https://deadtrees.earth/dataset/3712

this is very likely happening because of the added margins during mask vectorization.

please see this: https://github.com/cmosig/deadtreesmodels/blob/ea98c680904a0a11d3e0f149e6f5055b74bbc1b3/doitall.py#L89