Make MAX_PREV_WORD_COUNT_FOR_N_GRAM 2.

Bug: 14425059
Change-Id: Iefacd7e4a6c256658a58856240310eeb91ae32db
diff --git a/native/jni/src/defines.h b/native/jni/src/defines.h
index 57e1888..56d8bbb 100644
--- a/native/jni/src/defines.h
+++ b/native/jni/src/defines.h
@@ -338,7 +338,7 @@
 #define MAX_POINTER_COUNT_G 2
 
 // (MAX_PREV_WORD_COUNT_FOR_N_GRAM + 1)-gram is supported.
-#define MAX_PREV_WORD_COUNT_FOR_N_GRAM 1
+#define MAX_PREV_WORD_COUNT_FOR_N_GRAM 2
 
 #define DISALLOW_DEFAULT_CONSTRUCTOR(TypeName) \
   TypeName() = delete