Manifest for Android 8.1.0 Release 18 (OPM5.171019.017)

Change-Id: I92e7675c7e9d9bf6f149948ab8711c874dac96e5

default.xml

@@ -4,7 +4,7 @@
   <remote  name="aosp"
            fetch=".."
            review="https://android-review.googlesource.com/" />
-  <default revision="refs/tags/android-8.1.0_r17"
+  <default revision="refs/tags/android-8.1.0_r18"
            remote="aosp"
            sync-j="4" />