fix script to properly terminate docker-compose child
fix script to properly terminate docker-compose child

with previous approach, while docker-compose up was running,
bash would just wait on it, and be unable to invoke its trap handler.
apparently, when running the script interactively, ctrl-C would reach
docker-compose up directly, then invoke the trap handler,
but when running the script as subprocess, the signal wouldn't reach
anyone.

see
https://unix.stackexchange.com/questions/146756/forward-sigterm-to-child-in-bash

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