Add smooth loading for letter

src/components/Letters.vue

@@ -8,7 +8,7 @@
       <v-flex xs12 v-if="letters">
         <v-list>
           <template v-for="letter in letters">
-            <v-list-tile avatar v-bind:key="letter.url" :href="letter.link">
+            <v-list-tile avatar v-bind:key="letter.url" :to="letter.link">
               <v-list-tile-avatar>
                 <v-icon grey lighten-1 white--text>local_post_office</v-icon>
               </v-list-tile-avatar>