Fix code style by removing :fail from lower-type-bounds.md

[ayurchuk]

Existing documentation layout:


Expected one:

[heathermiller]

Ah! Thanks for catching this. Actually, I think the solution is for me to add tut:fail to this silly little Jekyll plugin I made so that this is correctly rewritten to a scala fenced code block after tut runs... Hang on, let me see...

[heathermiller]

@ayurchuk I think I got it! Fixed it in this little Jekyll plugin we have for making syntax highlighting place nicely with tut. See #860

Thank you so much for reporting this and for taking a first step at a fix! It's sincerely appreciated! ❤️