Override use of deprecated netstat on Linux.

[philliphoff]

So it looks like netstat is no longer installed by default on certain Linux distros (e.g. Ubuntu). This change moves to lsof instead (like on Mac).

Given we're now effectively overriding node-netstats handling on 2 out of 3 platforms (i.e. Mac and Linux), we should consider just handling the lsof ourselves and not be reliant on node-netstat at all. However, that's more of an extensive change that would have to wait.

Resolves #179.