fix convert underline to html style
bug #3 fix convert underline to html style (adam187)

This PR was squashed before being merged into the master branch (closes #3).

Discussion
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fix convert underline to html style

I had a problem with displaying results is Sismo.

    ( ! ) Notice: Undefined variable: text in Sismo/vendor/sensiolabs/ansi-to-html/SensioLabs/AnsiConverter/AnsiToHtmlConverter.php on line 112

It turns out that converting underline to html isn't properly done so i made this fix.

Commits
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2ff3a9c fix convert underline to html style