Clarify hook return value in "Custom Fields" documentation

[jonagoldman]

Its not clear just from reading the "Custom Fields" section inside "Route Object & Route Matching", that the hook must return something* in order for it to work.

I was learning about vue-router and read this section before reading about hooks.

[amirrustam]

@jonagoldman Actually this is addressed within http://vuejs.github.io/vue-router/en/pipeline/hooks.html under "Hook Resolution Rules," rule 3 . If the hook accepts the transition argument then it needs to continue the pipeline with transition.next(), otherwise it does not have to return anything.