FailSafeSocket doesn't change from online to offline

[z2mi]

Hi,
I ran client and server in 09-behavioral-design-patterns/02-state-failsafe-socket directory and It seems that FailSafeSocket never changes from online to offline state. We need some code in _safeWrite method in OnlineState to change state to offline if error happens.

[vbuzivskoy]

For some reason a socket doesn't emit 'error' event.

[shavidze]

you can see my solution:

[FranciscoMateusVG]

Created a PR to fix it.