Fix proguard flag file dependency.

Change-Id: I5dee31f40696fbfba2a9b2e07b48cd16f00fac14
diff --git a/Android.mk b/Android.mk
index 8c53458..5c33c33 100644
--- a/Android.mk
+++ b/Android.mk
@@ -10,6 +10,6 @@
 LOCAL_PACKAGE_NAME := UserDictionaryProvider
 LOCAL_CERTIFICATE := shared
 
-LOCAL_PROGUARD_FLAGS := -include $(LOCAL_PATH)/proguard.flags
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
 include $(BUILD_PACKAGE)