Missed icon content package rename

UPGRADING.md

@@ -67,7 +67,7 @@ New way:
 
 ```javascript
 import { library } from '@fontawesome/fontawesome-svg-core'
-import { fas } from '@fortawesome/fontawesome-free-solid'
+import { fas } from '@fortawesome/free-solid-svg-icons'
 import { faTwitter } from '@fortawesome/free-brands-svg-icons'
 import { FontAwesomeIcon } from '@fortawesome/vue-fontawesome'