Manifest for Android 8.1.0 Release 15 (OPM1.171019.021)

Change-Id: I56fd2d4a746e16404306a61390e64bddf666d28d
diff --git a/default.xml b/default.xml
index 952e92b..d04f598 100644
--- a/default.xml
+++ b/default.xml
@@ -4,7 +4,7 @@
   <remote  name="aosp"
            fetch=".."
            review="https://android-review.googlesource.com/" />
-  <default revision="refs/tags/android-8.1.0_r12"
+  <default revision="refs/tags/android-8.1.0_r15"
            remote="aosp"
            sync-j="4" />