fix(readme): update readme to use number version

Author: rhahao

README.md

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Deploy to Firebase
-        uses: sws2apps/firebase-deployment@e6dfe2cb17dbfeecf7910f5c1d4fee2f0c07deb5
+        uses: sws2apps/firebase-deployment@v2 #consider using pin for dependabot auto update
         with:
           project: 'my-firebase-project' #required
           config: 'frontend/firebase.json' #optional