Allow / suffix on invite URLs

This makes them a bit more clickable in some user agents (think
email, xmpp) which have to rely on parsing to find and highlight
URLs.

Fixes #48.

snikket_web/invite.py

@@ -48,6 +48,7 @@ def context() -> typing.Mapping[str, typing.Any]:
 
 
 @bp.route("/<id_>")
+@bp.route("/<id_>/")
 async def view(id_: str) -> str:
     try:
         invite = await client.get_public_invite_by_id(id_)