Fix proguard flag file dependency.

Change-Id: I26a639aea0e0b11ba65d621696c42e861847498e
diff --git a/java/Android.mk b/java/Android.mk
index e966fc7..03d48aa 100644
--- a/java/Android.mk
+++ b/java/Android.mk
@@ -17,6 +17,6 @@
 
 LOCAL_SDK_VERSION := current
 
-LOCAL_PROGUARD_FLAGS := -include $(LOCAL_PATH)/proguard.flags
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
 include $(BUILD_PACKAGE)