fix typo

Author: maltesander

modules/guides/pages/kubernetes-cluster-domain.adoc

@@ -4,7 +4,7 @@
 :dns-pod-service: https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/
 
 Stackable operators allow to configure a non-default cluster domain as described in {dns-custom-nameservers}[Customizing DNS Service] (and more in {dns-pod-service}[DNS for Services and Pods]).
-The configuration is primarily done via and environment variable `KUBERNETES_CLUSTER_DOMAIN`, but there is also a mechanism to auto detect the cluster domain using the `/etc/resolv.conf` file.
+The configuration is primarily done via an environment variable `KUBERNETES_CLUSTER_DOMAIN`, but there is also a mechanism to auto detect the cluster domain using the `/etc/resolv.conf` file.
 
 The following steps explain the use of the environment variable and the auto detection mechanism in detail: