Fix function routing

[lewisdaly]

There are a number of issues with routing:

• need to specify a trailing slash / for number (eg. https://dfstalk.vessels.tech/number/)
• the firebase hosting rerouting doesn't strip fields, meaning that /api/v1/number/ gets passed to the express router, which can't find the route. Perhaps this is something middleware can fix for us.
• related to this is now we need to specify /number/number/languages when using the us-central1-dfs-talk.cloudfunctions.net/ host, but /number/languages when using the dfstalk.vessels.tech host