sslServers should be closed after an inactivity period

[wisec]

Hi, I've experienced a port exhaustion error after a couple of days of using http-mitm-proxy on a high traffic network node. I found out that proxy.js opens a sslServer for each host on https and never closes them. Although you already answered on https://github.com/joeferner/node-http-mitm-proxy/issues/64 are there any plans to review sslServers design to overcome this issue? Thanks,