Replaced <kbd> element with <span> for the keyboard sequence.

[ghost]

Regarding Asciidoctor's Ruby code, the keyboard sequence element should not be <kbd> but <span>

Here is the ruby code from html5.rb :

def inline_kbd node
  if (keys = node.attr 'keys').size == 1
    %(<kbd>#{keys[0]}</kbd>)
  else
    key_combo = keys.map {|key| %(<kbd>#{key}</kbd>+) }.join.chop
    %(<span class="keyseq">#{key_combo}</span>)
  end
end

[mojavelinux]

👍 to aligning with the built-in HTML converter.

The reason we made this change was so that it was compatible with the styling of the <kbd> element in themes. If we nest the <kbd> elements, then the ornamentation gets compounded.