Fix rounded_cherry stem to properly use $stem_inner_slop

src/stems/rounded_cherry.scad

@@ -7,6 +7,6 @@ module rounded_cherry_stem(depth, slop, throw) {
 
     // inside cross
     // translation purely for aesthetic purposes, to get rid of that awful lattice
-    inside_cherry_cross(slop);
+    inside_cherry_cross($stem_inner_slop);
   }
 }