Child process is not killed on SIGTERM

[mkscrg]

cli.js does not kill the child process before exiting on SIGTERM.

Repro:

$ ./node_modules/.bin/flow server 2>/dev/null &
[1] 10415
$ kill -s SIGTERM 10415
$ ps ax | grep flow
10416 s002  S      0:00.85 .../node_modules/flow-bin/flow-osx-v0.57.3/flow server src
10417 s002  S      0:00.01 .../node_modules/flow-bin/flow-osx-v0.57.3/flow
10418 s002  S      0:00.01 .../node_modules/flow-bin/flow-osx-v0.57.3/flow
10419 s002  S      0:00.02 .../node_modules/flow-bin/flow-osx-v0.57.3/flow
10420 s002  S      0:00.01 .../node_modules/flow-bin/flow-osx-v0.57.3/flow
...