[tlbuild] asymptote 2.87 rebuild

[Karl Berry]

    warning [version]: using possibly incompatible version 2.85 of plain.asy

Thanks Robert. I haven't updated the runtime yet. Shortly.
I guess I'll try to make an x86_64-linux binary myself.

Meanwhile, John just sent me a tiny patch to picture.cc (committed),
relating to dvisvgm "optimization" in some way I don't understand :).
I don't think anyone besides you did the rebuild in the last couple
hours :).

Mojca ... please advise about CI ... --thanks, karl.