Fix entrypoint in sourced-ui-celery for dev

[dpordomingo]

When I tried the dev mode, I got:

$ sourced init local .
docker-compose working directory set to ~/.sourced/workdirs/local/L3Byb2plY3RzL3NyYy9naXRodWIuY29tL3NyYy1kL3NvdXJjZWQtY2U
[...]
Creating srcd-ymjsznno_sourced-ui-celery_1 ... error
[...]
ERROR: for sourced-ui-celery  Cannot start service sourced-ui-celery:
    OCI runtime create failed: container_linux.go:345:
    starting container process caused "exec: \"true\":
    executable file not found in $PATH": unknown
ERROR: Encountered errors while bringing up the project.
exit status 1

If I'm not wrong, true binary would be only accessible from /true

---

• I have updated the CHANGELOG file according to the conventions in keepachangelog.com
• This PR contains changes that do not require a mention in the CHANGELOG file