correct sdt objects of table of contents

src/file/table-of-contents/sdt-properties.ts

@@ -0,0 +1,9 @@
+import { XmlComponent } from "file/xml-components";
+import { Alias } from "./alias";
+
+export class SdtProperties extends XmlComponent {
+    constructor(alias: string) {
+        super("w:sdtPr");
+        this.root.push(new Alias(alias));
+    }
+}