Update SiPM mask hole dimensions

As reported by @halmamol, the size of the holes in the SiPM masks is 6x6 mm2, not 6x5 mm2

Author: gonzaponte

source/geometries/Next100SiPMBoard.cc

@@ -162,7 +162,7 @@ void Next100SiPMBoard::Construct()
   G4double mask_hole_length = mask_thickness_ - wls_thickness;
   G4double mask_hole_zpos   = - mask_thickness_/2. + mask_hole_length/2.;
   G4double mask_hole_x = 6.0 * mm;
-  G4double mask_hole_y = 5.0 * mm;
+  G4double mask_hole_y = 6.0 * mm;
 
   G4Box* mask_hole_solid_vol =
     new G4Box(mask_hole_name, mask_hole_x/2., mask_hole_y/2., mask_hole_length/2.);