Add missing if block to VR tutorial source example

Fixed formatting and corrected the example code to better reflect the intent of the tutorial text.
i.e.  "...The last thing we are doing in button_pressed is checking to see if the button pressed is 1..."

tutorials/vr/vr_starter_tutorial.rst

@@ -377,7 +377,8 @@ Add the following to ``VR_Controller.gd``:
         
         
         # If the menu button is pressed...
-        if grab_mode == "AREA":
+	if button_index == 1:
+		if grab_mode == "AREA":
 			grab_mode = "RAYCAST"
 			
 			if held_object == null: