Update task to use Map (#772)

* update task to use map

* Update README.md

Author: jenmerritt

map/download-preplanned-map/README.md

@@ -17,7 +17,7 @@ Select a map area from the Preplanned Map Areas list. Click the Download button
 ## How it works
 
 1. Open the online `ArcGISMap` from a `PortalItem` and display it.
-2. Create an `OfflineMapTask` using the portal item.
+2. Create an `OfflineMapTask` using the map.
 3. Get the `PreplannedMapArea`s from the task, and then load them.
 4. To download a selected map area, create the default `DownloadPreplannedOfflineMapParameters` from the task using the selected preplanned map area.
 5. Set the update mode of the preplanned map area.

map/download-preplanned-map/src/main/java/com/esri/samples/download_preplanned_map/DownloadPreplannedMapController.java

@@ -91,8 +91,8 @@ private void initialize() {
       areaOfInterestRenderer.setSymbol(areaOfInterestLineSymbol);
       areasOfInterestGraphicsOverlay.setRenderer(areaOfInterestRenderer);
 
-      // create an offline map task for the portal item
-      offlineMapTask = new OfflineMapTask(portalItem);
+      // create an offline map task for the map
+      offlineMapTask = new OfflineMapTask(onlineMap);
 
       // use a cell factory which shows the preplanned area's title
       preplannedAreasListView.setCellFactory(c -> new PreplannedMapAreaListCell());