userguide: fix too short title underline

user_guide_src/source/testing/response.rst

@@ -224,7 +224,7 @@ Finally, you can check if a checkbox exists and is checked with the ``seeCheckbo
    :lines: 2-
 
 seeXPath()
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+----------
 
 You can use ``seeXPath()`` to take advantage of the full power that xpath gives you.
 This method is aimed at more advanced users who want to write a more complex expressions