href prop isnt needed if object in to prop

If you use an object in to prop without using the href prop (for example if you use named routes) you will get href="http://github.com/[object%20Object]" in your html.
My pullrequest will fix this.

Author: jjonas-gcs

components/nav-item.vue

@@ -3,7 +3,7 @@
         <component
                 :class="classObject"
                 @click="onclick"
-                :href="href || to"
+                :href="hrefString"
                 :is="componentType"
                 active-class="active"
                 :to="to"
@@ -28,6 +28,9 @@
             },
             componentType() {
                 return this.to ? 'router-link' : 'a';
+            },
+            hrefString() {
+                return typeof this.to === 'object' ? this.href || undefined : this.href || this.to;
             }
         },
         props: {