Update firebase-migration-rest.md

FCM V1 was mentioned as FCM C1, hence it is updated now.

Author: rajesh-Microsoft

articles/notification-hubs/firebase-migration-rest.md

@@ -186,7 +186,7 @@ If you have an existing GCM registration, update the registration to **FcmV1Regi
 </entry>
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-#### Option 2: Create FCM c1 installation or update GCM installation to FCM v1
+#### Option 2: Create FCM V1 installation or update GCM installation to FCM v1
 
 See [Create or overwrite an installation](/rest/api/notificationhubs/create-overwrite-installation) and set `platform` to `FCMV1`.