manifest: change android revision to android-8.1.0_r7

Change-Id: I14961838c20e33c1bf61821754a2437da10e18dd
diff --git a/default.xml b/default.xml
index 5d49cb1..9fa936a 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_r1"
+  <default revision="refs/tags/android-8.1.0_r7"
            remote="aosp"
            sync-c="true"
            sync-j="12" />