can't add alias: '' to s child route (to make it behave like a default route.

[LinusBorg]

Repro: https://jsfiddle.net/p7uk1pbv/1/

The other way around works: https://jsfiddle.net/p7uk1pbv/2/

Cause: https://github.com/vuejs/vue-router/blob/dev/src/create-route-map.js#L62

[nicolas-t]

initial message #803

[LinusBorg]

PR submitted.