allow router mode to be set in config

lib/app/router.js

@@ -54,7 +54,7 @@ const scrollBehavior = (to, from, savedPosition) => {
 <% } %>
 
 export default new Router({
-  mode: 'history',
+  mode: '<%= router.mode %>',
   base: '<%= router.base %>',
   linkActiveClass: '<%= router.linkActiveClass %>',
   scrollBehavior,

lib/nuxt.js

@@ -36,6 +36,7 @@ class Nuxt {
         mode: 'out-in'
       },
       router: {
+        mode: 'history',
         base: '/',
         middleware: [],
         linkActiveClass: 'nuxt-link-active',