Added Admiral to ADOPTERS.md
* [Infoblox](https://www.infoblox.com) uses CoreDNS in its Active Trust Cloud SaaS service, as well as for Kubernetes cluster DNS.
* [Sky Betting & Gaming](http://engineering.skybettingandgaming.com) uses CoreDNS for Kubernetes cluster DNS.
* [Kismia](https://kismia.com) uses CoreDNS for Kubernetes cluster DNS.
+* [Admiral](https://getadmiral.com) uses CoreDNS to handle geographic DNS requests for our public-facing microservices.
