Fixed insert_hole() convexity

vitamins/insert.scad

@@ -78,7 +78,8 @@ module insert(type) { //! Draw specified insert
 module insert_hole(type, counterbore = 0, horizontal = false) { //! Make a hole to take an insert, ```counterbore``` is the extra length for the screw
     h = insert_hole_length(type);
 
-    render() if(horizontal) {
+    render(convexity = 2)
+        if(horizontal) {
             teardrop_plus(r = insert_hole_radius(type), h = 2 * h);
 
             if(counterbore)