doc: update lts description in the collaborator guide
doc: update lts description in the collaborator guide

PR-URL: https://github.com/nodejs/node/pull/3668
Reviewed-By: Julien Gilli <498f087c128f7ba877a9c41cd8ff0767d4a0d56c@fastmail.fm>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node