Replace , with . in gui_containers.rst

Author: ershn

tutorials/ui/gui_containers.rst

@@ -6,7 +6,7 @@ Using Containers
 ================
 
 :ref:`Anchors <doc_size_and_anchors>` are an efficient way to handle
-different aspect ratios for basic multiple resolution handling in GUIs,
+different aspect ratios for basic multiple resolution handling in GUIs.
 
 For more complex user interfaces, they can become difficult to use.