Allows to define 0 reconnections

I changed the constructor condition to accept 0 max_connect_retries and
I also changed the counter to manage 0 accordingly and use any negative
number as infinite retries
Merge branch 'if-allow-0-max-conn-retries' of github.com:ifraixedes/winston-logstash into ifraixedes-if-allow-0-max-conn-retries

Conflicts:
	lib/winston-logstash.js