Streams not closing properly

[jldowns]

When chaining many .then() blocks, I get

Error: (SSH) Channel open failure: open failed

due to hitting the max number of connections to my remote server. I think this is the same issue as mscdex/ssh2#219 . I added some .close() calls before the Promise resolutions and it solved my problem.

I'll submit a pull request with what worked for me, although I don't have any test scripts to run it against.

[steelbrain]

Fixed by #22