Add node v6 to travis and change 4.0, 5.0 to 4.x, 5.x
Add node v6 to travis and change 4.0, 5.0 to 4.x, 5.x

getsentry/raven-node,getsentry/raven-node,miguelb/raven-node,getsentry/raven-js,getsentry/raven-js,miguelb/raven-node,getsentry/raven-js,getsentry/raven-js,BuildingConnected/raven-node