fix error TS2339: Property 'getModellingRule' does not exist on type

'UAObject'

src/ua/UABaseNode.ts

@@ -110,6 +110,15 @@ export class UABaseNode implements IToXML{
         return children;
     }
 
+    getModellingRule(): string|undefined{
+        this.references.forEach((ref)=>{
+            if(ref.referenceType == "HasModellingRule"){
+                return ref.toNode.displayName;
+            }
+        });
+        return undefined;
+    }
+
     resolveReferences(nm: Map<string, UABaseNode>) {
         for(const ref of this.references) {
             const fromNode=nm.get(ref.fromRef.toString())