Fix proguard flag file dependency.

Change-Id: I4edb3ee225332434f74d016cfffa8d95d88b9bcd
diff --git a/Android.mk b/Android.mk
index d574b3f..5a820bd 100644
--- a/Android.mk
+++ b/Android.mk
@@ -10,7 +10,7 @@
 LOCAL_PACKAGE_NAME := Contacts
 LOCAL_CERTIFICATE := shared
 
-LOCAL_PROGUARD_FLAGS := -include $(LOCAL_PATH)/proguard.flags
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
 include $(BUILD_PACKAGE)