added xmlKeys to xmlcomponent

ts/docx/paragraph/properties.ts

@@ -2,6 +2,10 @@ import {XmlComponent, Attributes} from "../xml-components";
 
 export class ParagraphProperties implements XmlComponent {
     private pPr: Array<XmlComponent>;
+    
+    xmlKeys = {
+        pPr: 'w:rPr'
+    }
 
     constructor() {
         this.pPr = new Array<XmlComponent>();