Update Docker command for Config Server discovery-first (#429)

Without the additional switch, tests fail in WSL2, because Config Server registers itself in Eureka using `host.docker.internal`, which is inaccessible when running inside WSL2/Ubuntu.

Author: bart-vmware

CommonTasks.md

@@ -32,7 +32,7 @@ docker run --rm -it --pull=always -p 8888:8888 -v $PWD/steeltoe/config-repo:/con
 To start a config server that registers itself with Eureka at startup (discovery-first):
 
 ```shell
-docker run --rm -it --pull=always -p 8888:8888 --name steeltoe-config -e eureka.client.enabled=true steeltoe.azurecr.io/config-server
+docker run --rm -it --pull=always -p 8888:8888 --name steeltoe-config -e eureka.client.enabled=true -e eureka.instance.hostname=localhost steeltoe.azurecr.io/config-server
 ```
 
 To start a config server that requires basic authentication (and change username and password from the defaults of devuser/devpassword):