outputs are interleaved when newlines are missing

[milahu]

$ node bin/concurrently.js --names x,o "bash -c \"while true; do printf x; sleep 0.2; done\"" "bash -c \"while true; do printf o; sleep 0.2; done\""
[x] xoxoxoxoxoxoxoxoxoxoxoxoxoxoxoxoxo^Cbash -c "while true; do printf x; sleep 0.2; done" exited with code SIGINT
[o] bash -c "while true; do printf o; sleep 0.2; done" exited with code SIGINT

expected: flush early, dont wait for newline + remember last command to continue line

[x] x
[o] o
[x] x
[o] o

slightly related to #168

would be easy to solve with #247