Change name of DecayingUtils.

Bug: 6669677
Change-Id: I97839b2184b95ae1659c55a9b31d22e2d601cba1
diff --git a/native/jni/Android.mk b/native/jni/Android.mk
index 36afea5..ca6a779 100644
--- a/native/jni/Android.mk
+++ b/native/jni/Android.mk
@@ -85,8 +85,8 @@
     $(addprefix suggest/policyimpl/dictionary/utils/, \
         buffer_with_extendable_buffer.cpp \
         byte_array_utils.cpp \
-        decaying_utils.cpp \
         dict_file_writing_utils.cpp \
+        forgetting_curve_utils.cpp \
         format_utils.cpp) \
     suggest/policyimpl/gesture/gesture_suggest_policy_factory.cpp \
     $(addprefix suggest/policyimpl/typing/, \