Made it so the folders only get ingored in the root

With the current setup these folders are ignored in the whole repo, but they're only automatically generated in the project root so it makes sense to only ignore the ones in the root.

I made this change because one of the assets in my project uses a folder called 'Library', and I was wondering why it never uploaded that folder.

Author: Tandoori

Unity.gitignore

@@ -1,7 +1,7 @@
-[Ll]ibrary/
-[Tt]emp/
-[Oo]bj/
-[Bb]uild/
+/[Ll]ibrary/
+/[Tt]emp/
+/[Oo]bj/
+/[Bb]uild/
 
 # Autogenerated VS/MD solution and project files
 *.csproj