Print graph with special color/marker for failed commands

[pothos]

With --cmd the length may vary because the command failed to run some times. This can be the case with a typical curl -fsSL invocation.

It would be nice to have the graph show this through a different color or marker (e.g., an × instead of a dot).

[myarcana]

https://github.com/orf/gping/issues/409 is the same issue but for ping instead of commands.