Changing <PathFollow> to <PathFollow3D>

Small change so the C# code so it compiles.

getting_started/first_3d_game/05.spawning_mobs.rst

@@ -250,7 +250,7 @@ Let's code the mob spawning logic. We're going to:
 
         // Choose a random location on the SpawnPath.
         // We store the reference to the SpawnLocation node.
-        var mobSpawnLocation = GetNode<PathFollow>("SpawnPath/SpawnLocation");
+        var mobSpawnLocation = GetNode<PathFollow3D>("SpawnPath/SpawnLocation");
         // And give it a random offset.
         mobSpawnLocation.ProgressRatio = GD.Randf();