bump version to 4.2.1

Change-Id: If8206ec632b4e912433eebdfa4aed8dde8f37cb4
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 1162b78..fb1f361 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -41,7 +41,7 @@
   # which is the version that we reveal to the end user.
   # Update this value when the platform version changes (rather
   # than overriding it somewhere else).  Can be an arbitrary string.
-  PLATFORM_VERSION := 4.2
+  PLATFORM_VERSION := 4.2.1
 endif
 
 ifeq "" "$(PLATFORM_SDK_VERSION)"