Fix proguard.flags to keep method for testing

Change-Id: Iab6c9a4104e8eec3eeb55fdb063d4368338ac74d
diff --git a/java/proguard.flags b/java/proguard.flags
index 33af890..caf1ea1 100644
--- a/java/proguard.flags
+++ b/java/proguard.flags
@@ -35,6 +35,6 @@
   *;
 }
 
--keep class com.android.inputmethod.keyboard.internal.MiniKeyboardBuilder$MiniKeyboardParams {
+-keep class com.android.inputmethod.keyboard.MiniKeyboard$Builder$MiniKeyboardParams {
   <init>(...);
 }