update NxLibraryDimensionDef

fix missing qLabelExpression https://help.qlik.com/en-US/sense-developer/June2018/APIs/EngineAPI/definitions-NxLibraryDimensionDef.html

types/qlik-engineapi/index.d.ts

@@ -392,6 +392,11 @@ declare namespace EngineAPI {
          * Array of dimension labels.
          */
         qFieldLabels: string[];
+
+        /**
+         * no docu
+         */
+        qLabelExpression: string;
     }
 
     /**