Update getting-started.md (#1601)

When following the documentation to try and implement Firebase for a Nuxt project I stumbled on a typo where the import for a database reference was a written as `import { getDatabase, dbRef } from 'firebase/database'` as opposed to `import { getDatabase, ref as dbRef } from 'firebase/database'` as the rest of the document

Author: Zadigo

Diff for: docs/guide/getting-started.md

@@ -38,7 +38,7 @@ Most of the time, you should gather collection references in one of your files a
 
 ```js
 import { initializeApp } from 'firebase/app'
-import { getDatabase, dbRef } from 'firebase/database'
+import { getDatabase, ref as dbRef } from 'firebase/database'
 // ... other firebase imports
 
 export const firebaseApp = initializeApp({