How to prevent app from showing its update in play store using titanium backup?
I'll give you a good alternative for that

If you don't want to ever update the app even after you reset your phone and reinstall it without involving the Google Play Store settings. Grab an app called APK Editor from here. Install and run it, 


Click on Select apk from App
Identify the app you don't want updated
Click it and chose common edit
Edit the package name section
Press done
Reinstall the app
Delete the original app


Google Play Store won't tell you any updates for it forever