Update to vue.mdx (#2609)

import CarbonComponentsVue from '@carbon/vue'; has wider acceptability (codesandbox.io/NuxtJS) than pointing to index under src folder

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

src/pages/developing/frameworks/vue.mdx

@@ -81,7 +81,7 @@ carbon styles and components.
 
 ```js
 import 'carbon-components/css/carbon-components.css';
-import CarbonComponentsVue from '@carbon/vue/src/index';
+import CarbonComponentsVue from '@carbon/vue';
 Vue.use(CarbonComponentsVue);
 ```