Prometheus config may reference incorrect [service] names

[DazWilkin]

https://github.com/google/keytransparency/blob/master/deploy/prometheus/prometheus.yml

References hostnames kt-server and kt-signer:

...
scrape_configs:
  - job_name: 'kt-server'
    static_configs:
        - targets: ['kt-server:8081']
  - job_name: 'kt-signer'
    static_configs:
        - targets: ['kt-signer:8081']

I think these should now be server and sequencer respectively:

...
scrape_configs:
  - job_name: 'server'
    static_configs:
        - targets: ['server:8081']
  - job_name: 'sequencer'
    static_configs:
        - targets: ['sequencer:8081']