fires postinstall: gitbook install

[izelnakri]

Which causes an install error if gitbook binary is not available on the machine.

[izelnakri]

https://github.com/psastras/node-threadpool/blob/v1.5.5/package.json#L35 please publish master to npm

[sblackstone]

if not remove, gitbook install || true

[hhu8]

this issue not fixed yet.