Bump update_engine version to 9

This enables lz4diff

Test: th
Bug: 295440534
Change-Id: I96fda44ca2ea644c1b5921f34fc5736d881e7826
diff --git a/update_engine.conf b/update_engine.conf
index 2d3a655..22b59d9 100644
--- a/update_engine.conf
+++ b/update_engine.conf
@@ -1,2 +1,2 @@
 PAYLOAD_MAJOR_VERSION=2
-PAYLOAD_MINOR_VERSION=8
+PAYLOAD_MINOR_VERSION=9