Cannot install homebridge-harmony module on Mac
When I install Homebridge-harmony (using the command):

`
sudo npm install -g homebridge-harmony@beta
`

The installation creates the "homebridge-harmony" folder in /usr/local//lib/node_modules then (at the installation end), the folder is removed and this error is returned:

`
no such file or directory, chmod '/usr/local/lib/node_modules/homebridge-harmony/node_modules/sshpk/bin/sshpk-conv'
`
`
This is related to npm not being able to find a file
`

Installation is fine on raspberry pi but fails on Mac mini.

Running:
- MacOSX v10.10.5
- node v8.3.11
- homebridge v.0.4.43

