Go to Other tab and set the "horizontal size compensation" to -0.1mm. That will make all your holes bigger.
Read more about it here: viewtopic.php?f=8&t=2042
Of cause this is a nice feature. But I think the Slicer does something wrong.
All models which I've printed have a perfect outer measurement ( < .1mm deviation) but the holes, no matter if they are round or rectangular, were about 0.2-0.3mm smaller. This is the same issue all other slicers have. A hole somewhere in the model is always smaller. It is like the slicer don't consider the width of the extruded trace in the inner outlines. A hole with 3mm diameter gets 2.8mm, a hole with 15mm gets 14.8mm. Of cause the horizontal size compensation can correct this, but I think it is the wrong way to correct this issue.
I want to design models as I need them and the slicer has to consider what the real diameter after print would look like