Output syntax on ocaml code blocks has changed

[panglesd]

Since ocaml/odoc#1149, mdx is not up to date with regards to the syntax for output of the execution of OCaml code blocks:

• there must be no delimiter at the end of the output block this is already up to date
• there must be a delimiter in order to have an output block, see Bad parsing or ][ in block code ocaml/odoc#1137.