use LinkedHashMap for allOf and properties to maintain insertion order

Author: ivangsa

src/main/java/io/zenwave360/jsonrefparser/$RefParser.java

@@ -216,8 +216,8 @@ private void merge(AllOfObject allOfObject, Map<String, Object> item) {
     }
 
     private static class AllOfObject {
-        Map<String, Object> allOf = new HashMap<>();
-        Map<String, Object> properties = new HashMap<>();
+        Map<String, Object> allOf = new LinkedHashMap<>();
+        Map<String, Object> properties = new LinkedHashMap<>();
         List<String> required = new ArrayList<>();