Spago should respect TERM=dumb or TERM=win

[bbarker]

See e.g. 9fans/plan9port#180 (comment)

I'd like to disable escape sequences from output when not using spago from a live terminal, e.g., for logging.

[f-f]

@bbarker great point 👍

Does using --no-color work for now?

[bbarker]

Yes, thanks for pointing that out! I was using an older version of spago in my container that didn't have that option.

[f-f]

Fix up in #581