Use json as env variable for firebase admin service account (#25)

.env variable value is a JSON string that is the contents of the key file

pkgs/hanzo-auth/lib/firebase/firebase-admin.ts

@@ -9,7 +9,7 @@ export const firebaseApp =
   getApps().find((it) => it.name === 'firebase-admin-app') ||
   initializeApp(
     {
-      credential: cert(process.env.FIREBASE_ADMIN_SERVICE_ACCOUNT!),
+      credential: cert(JSON.parse(process.env.FIREBASE_ADMIN_SERVICE_ACCOUNT!)),
     },
     'firebase-admin-app'
   )