Doesn't work when MultiMarkdown is installed

[Alexander Kucera]

Hi guys,

I just stumbled across this issue and have a fix for it. However I have no idea how to push pull request, so here it is in plain text.

In Info.plist add <string>net.multimarkdown.text</string> to the LSItemContentTypes array.

So:

        <array>
            <string>net.daringfireball.markdown</string>
            <string>org.vim.markdown-file</string>
        </array>

Becomes:

        <array>
            <string>net.daringfireball.markdown</string>
            <string>net.multimarkdown.text</string>
            <string>org.vim.markdown-file</string>
        </array>

[Aeryn Riley Dowling-Toland]

Thanks. I have updated the code.