android: update to android-8.1.0_r11

Change-Id: I9213864fb71b2d5c3a718cbfbab5482ca0a60442
diff --git a/default.xml b/default.xml
index 9fa936a..4a0c68b 100644
--- a/default.xml
+++ b/default.xml
@@ -3,7 +3,7 @@
   <remote  name="aosp"
            fetch="https://android.googlesource.com"
            review="https://android-review.googlesource.com/" />
-  <default revision="refs/tags/android-8.1.0_r7"
+  <default revision="refs/tags/android-8.1.0_r11"
            remote="aosp"
            sync-c="true"
            sync-j="12" />