Suppress pointless warning

It's an undocomented package private method after all.

src/nl/jeroenhoek/josm/gridify/GridifyAction.java

@@ -193,6 +193,7 @@ Optional<InputData> inputDataFromSelection(Collection<OsmPrimitive> selection) {
         return Optional.empty();
     }
 
+    @SuppressWarnings("MixedMutabilityReturnType")
     List<Node> nodesBetween(Node start, Node stop, int n) {
         if (n < 1) return Collections.emptyList();