fix: last line is never sent

[greut]

I've been experimenting with the streaming option and it seems that it misses the last line if that one isn't terminated by a carriage return.

[coveralls]

Coverage decreased (-1.0%) to 99.035% when pulling fe4165a on greut:flush-then-close into a151197 on go-cmd:master.

[coveralls]

Coverage remained the same at 100.0% when pulling b66c7d8 on greut:flush-then-close into a151197 on go-cmd:master.

[daniel-nichter]

Sorry for the slow response. Thanks for the fix, PR, and test! I'll merge and tweak the test a little: keep the original, then add a new one specifically for this.