update preview version number to 2 for offline docs

Change-Id: I56cab8d21f9521fab17ec79a441c518cf9da536c
diff --git a/Android.mk b/Android.mk
index 1e541f3..3f0dad1 100644
--- a/Android.mk
+++ b/Android.mk
@@ -874,7 +874,7 @@
 		-hdf sdk.preview.version 1 \
 		-hdf sdk.version $(framework_docs_SDK_VERSION) \
 		-hdf sdk.rel.id $(framework_docs_SDK_REL_ID) \
-		-hdf sdk.preview 1
+		-hdf sdk.preview 2
 
 # ====  the api stubs and current.xml ===========================
 include $(CLEAR_VARS)