Bump PLATFORM_PREVIEW_SDK_VERSION to 4

Change-Id: Ia44cfc3ff839c9ec84aec32e37c42b96de67075e
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index e88623e..25dfcdc 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -80,7 +80,7 @@
     # assuming the device can only support APIs as of the previous official
     # public release.
     # This value will always be 0 for release builds.
-    PLATFORM_PREVIEW_SDK_VERSION := 3
+    PLATFORM_PREVIEW_SDK_VERSION := 4
   endif
 endif