[now-cli] Don't throw if builder child process can not be killed (#3192)
[now-cli] Don't throw if builder child process can not be killed (#3192)

The Sentry error reports that the process has already been killed, so no need to throw in this case.

Fixes #3191.
zeit/now-cli,zeit/now-cli,zeit/now-cli,zeit/now-cli,zeit/now-cli,zeit/now-cli,zeit/now-cli