Ignore changelog file

changelog.txt should only exit in Unity Asset Store package.

changelog or release note for repository should be documented in master
branch (release branch) commit log and GitHub release page.

Author: lawwong

.gitignore

@@ -13,6 +13,8 @@ ProjectSettings/*
 Assets/*
 !Assets/HTC.UnityPlugin/
 !Assets/HTC.UnityPlugin.meta
+Assets/HTC.UnityPlugin/ViveInputUtility/changelog.txt
+Assets/HTC.UnityPlugin/ViveInputUtility/changelog.txt.meta
 
 *.cfg