Manifest for Android 8.1.0 Release 4 (OPM1.171019.013)

Change-Id: I109aa16a8853cf64291bcc0d64e75d8b915de8ae
diff --git a/default.xml b/default.xml
index 0a87eab..b9d3ede 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_r3"
+  <default revision="refs/tags/android-8.1.0_r4"
            remote="aosp"
            sync-j="4" />