fix hangs with CLI commands waiting for input

[silverwind]

The previous .resume() and .pipe() did not close the stdin stream on the child process which made scripts that wait for data on stdin hang. The fix manually sends all stdin chunks to the child and ensures that the stream is always closed afterwards.

There might be a cleaner solution using flowing mode, but I'm not sure how to ensure closure of the target WriteStream when using .pipe().

This should properly solve these issue:

• Git-command stuck #95
• process hangs when spawned through child_process raineorshine/npm-check-updates#119

[silverwind]

Actually, there seems to be an issue when sending big amounts of data on stdin, investigating.

[silverwind]

I have to rethink this. I'm pretty certain the issue could be fixed on get-stdin's side too, but hopefully not with a timeout like in sindresorhus/get-stdin#19.