Replace deprecated method

Signed-off-by: Ravi Nadahar <nadahar@rediffmail.com>

Author: Ravi Nadahar

bundles/org.openhab.core.model.yaml/src/main/java/org/openhab/core/model/yaml/internal/YamlModelRepositoryImpl.java

@@ -252,7 +252,7 @@ private boolean processModelContent(String modelName, Kind kind, JsonNode fileCo
 
         List<String> newElementNames = new ArrayList<>();
         // get sub-elements
-        Iterator<Map.Entry<String, JsonNode>> it = fileContent.fields();
+        Iterator<Map.Entry<String, JsonNode>> it = fileContent.properties().iterator();
         while (it.hasNext()) {
             Map.Entry<String, JsonNode> element = it.next();
             String elementName = element.getKey();