update API version to 9

Change-Id: Ia573996bb910e19c8f7017ca13cf9d9d77083404
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index a30b7d9..5618d78 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -53,7 +53,7 @@
   # intermediate builds).  During development, this number remains at the
   # SDK version the branch is based on and PLATFORM_VERSION_CODENAME holds
   # the code-name of the new development work.
-  PLATFORM_SDK_VERSION := 8
+  PLATFORM_SDK_VERSION := 9
 endif
 
 ifeq "" "$(PLATFORM_VERSION_CODENAME)"