update preview overview and update images.

Change-Id: Ie4c37f5895e15313cc4dd58ef72a8fcd5ab20189
diff --git a/docs/html/preview/api-overview.jd b/docs/html/preview/api-overview.jd
index df18330..36341b2 100644
--- a/docs/html/preview/api-overview.jd
+++ b/docs/html/preview/api-overview.jd
@@ -1,7 +1,7 @@
 page.title=Android N APIs & Features
 meta.tags="preview", "androidn"
 page.tags="preview", "developer preview"
-page.image=images/cards/card-n-overview_2x.png
+page.image=images/cards/card-n-apis_2x.png
 @jd:body
 
 <p>