fix #200 generalize boundaries line features

Author: nvkelso

tiles/src/main/java/com/protomaps/basemap/layers/Boundaries.java

@@ -276,10 +276,15 @@ public List<OsmRelationInfo> preprocessOsmRelation(OsmElement.Relation relation)
 
   @Override
   public List<VectorTile.Feature> postProcess(int zoom, List<VectorTile.Feature> items) {
+    var tolerance = 0.4;
+    if( zoom < 6 ) {
+      tolerance = 0.2;
+    }
     return FeatureMerge.mergeLineStrings(items,
       0.0,
-      0.1,
-      4
+      tolerance,
+      4,
+      true
     );
   }