fix(config): Use a more generic server url pattern for push registrations.
fix(config): Use a more generic server url pattern for push registrations.

https://github.com/mozilla/fxa-auth-server/pull/1699

r=philbooth
eoger/fxa-auth-server,eoger/fxa-auth-server,mozilla/fxa-auth-server,mozilla/fxa-auth-server,mozilla/fxa-auth-server,eoger/fxa-auth-server,eoger/fxa-auth-server,mozilla/fxa-auth-server