Update components.md (#1147) (#375)
Update components.md (#1147) (#375)

To fix circular reference in webpack, change `require('./tree-folder-contents.vue').default` to `require('./tree-folder-contents.vue')`
my env:
```
nodejs: 6.9.1
vuejs: 2.3.4
webpack: 2.7.1
```
potato4d/jp.vuejs.org,potato4d/jp.vuejs.org,vuejs/jp.vuejs.org,vuejs/jp.vuejs.org