Remove limit for sockets per connection to fix "Premature close" error + prepare patch release

[kravets-levko]

Fixes #208

[susodapop]

Stamping for now. Is there any possibility of a runaway condition where we recursively create many, many more sockets?

[kravets-levko]

maxSockets: Infinity is basically a default value since some very early Node version, I just made it more explicit. In combination with socket timeout, I think Node can deal with it. In the worst case, user will get some error when system limit reached. Also, later we're going to make Agent customizable and allow user to tweak those settings