Minor improvements to the optional syntax page

[josevalim]

We use do/end in Elixir, so I reverted to that, but I don't oppose moving to do-end as long as we are consistent. :)

[josevalim]

:green_heart: :blue_heart: :purple_heart: :yellow_heart: :heart:

[lexmag]

We use do/end in Elixir, so I reverted to that, but I don't oppose moving to do-end as long as we are consistent. :)

Indeed, we also have do/end occurrences. I'll standardize everything on do-end then (it reads like a continuous block, while / can be perceived as a choice; of course, the exact context makes it less problematic but still).