csv: fix import for saveAs shim

After switch from systemjs to webpack, needed to import the
file-saver saveAs shim for it work. Fixes #9525

public/app/core/utils/file_export.ts

 import _ from 'lodash';
 import moment from 'moment';
-
-declare var window: any;
+import {saveAs} from 'file-saver';
 
 const DEFAULT_DATETIME_FORMAT = 'YYYY-MM-DDTHH:mm:ssZ';
 
@@ -69,5 +68,5 @@ export function exportTableDataToCsv(table, excel = false) {
 
 export function saveSaveBlob(payload, fname) {
     var blob = new Blob([payload], { type: "text/csv;charset=utf-8" });
-    window.saveAs(blob, fname);
+    saveAs(blob, fname);
 }