misc: migrate to vuetify 2.0 (wip)

client/components/admin/admin-stats.vue

@@ -4,7 +4,7 @@
       v-flex(xs12)
         .admin-header-icon: v-icon(size='80', color='grey lighten-2') show_chart
         .headline.primary--text Statistics
-        .subheading.grey--text Useful information about your wiki
+        .subtitle-1.grey--text Useful information about your wiki
         .pa-3
           fingerprint-spinner(
             :animation-duration='1500'