Redo naming in Service concept

Write “primary” in place of “master”.

Author: Tim Bannister

content/en/docs/concepts/services-networking/service.md

@@ -503,18 +503,18 @@ It also supports variables (see [makeLinkVariables](https://github.com/kubernete
 that are compatible with Docker Engine's
 "_[legacy container links](https://docs.docker.com/network/links/)_" feature.
 
-For example, the Service `redis-master` which exposes TCP port 6379 and has been
+For example, the Service `redis-primary` which exposes TCP port 6379 and has been
 allocated cluster IP address 10.0.0.11, produces the following environment
 variables:
 
 ```shell
-REDIS_MASTER_SERVICE_HOST=10.0.0.11
-REDIS_MASTER_SERVICE_PORT=6379
-REDIS_MASTER_PORT=tcp://10.0.0.11:6379
-REDIS_MASTER_PORT_6379_TCP=tcp://10.0.0.11:6379
-REDIS_MASTER_PORT_6379_TCP_PROTO=tcp
-REDIS_MASTER_PORT_6379_TCP_PORT=6379
-REDIS_MASTER_PORT_6379_TCP_ADDR=10.0.0.11
+REDIS_PRIMARY_SERVICE_HOST=10.0.0.11
+REDIS_PRIMARY_SERVICE_PORT=6379
+REDIS_PRIMARY_PORT=tcp://10.0.0.11:6379
+REDIS_PRIMARY_PORT_6379_TCP=tcp://10.0.0.11:6379
+REDIS_PRIMARY_PORT_6379_TCP_PROTO=tcp
+REDIS_PRIMARY_PORT_6379_TCP_PORT=6379
+REDIS_PRIMARY_PORT_6379_TCP_ADDR=10.0.0.11
 ```
 
 {{< note >}}