11988.md

Every underline type except `none` is read as underlined text, not
only `single`.

```
% pandoc command/11988.docx -t native
^D
[ Para
    [ Underline
        [ Str "single"
        , Space
        , Str "double"
        , Space
        , Str "thick"
        , Space
        , Str "dotted"
        , Space
        , Str "wave"
        , Space
        , Str "words"
        ]
    , Space
    , Str "none"
    ]
]
```