Add feathers-vuex in ecosystem dropdown

Author: daffl

.vuepress/config.js

@@ -126,6 +126,9 @@ module.exports = {
         }, {
           text: 'YouTube Playlist',
           link: 'https://www.youtube.com/playlist?list=PLwSdIiqnDlf_lb5y1liQK2OW5daXYgKOe'
+        }, {
+          text: 'Feathers VueX',
+          link: 'https://vuex.feathersjs.com/'
         }, {
           text: 'Previous versions',
           items: [{