manifest: android-9.0.0_r16 -> android-9.0.0_r21

Change-Id: Iec63dd87b6382512ec4f94a52eeef8a4674b8576
diff --git a/default.xml b/default.xml
index 00d872f..57bd0af 100644
--- a/default.xml
+++ b/default.xml
@@ -11,7 +11,7 @@
   <remote  name="aosp"
            fetch="https://android.googlesource.com"
            review="android-review.googlesource.com"
-           revision="refs/tags/android-9.0.0_r16" />
+           revision="refs/tags/android-9.0.0_r21" />
 
   <default revision="refs/heads/lineage-16.0"
            remote="github"