Fixed Invoker configuration (#18)

* Fixed Invoker configuration
* Invoker was failing to start as it was referencing to incorrect property name “WHISK_API_HOST”.
* Changed it to correct property name “WHISK_API_HOST_NAME”.
diff --git a/docker-compose/docker-compose.yml b/docker-compose/docker-compose.yml
index d461896..9504daf 100644
--- a/docker-compose/docker-compose.yml
+++ b/docker-compose/docker-compose.yml
@@ -86,7 +86,7 @@
     ports:
       - "8888:8888"
 
-  # WHISK INVOKER AGENT
+  # WHISK INVOKER AGENT 
   invoker:
     image: whisk/invoker:latest
     command: /bin/sh -c "/invoker/bin/invoker 0 >> /logs/invoker-local_logs.log 2>&1"
@@ -126,7 +126,7 @@
 
       INVOKER_CONTAINER_NETWORK: openwhisk_default
 
-      WHISK_API_HOST: https://${DOCKER_COMPOSE_HOST}
+      WHISK_API_HOST_NAME: https://${DOCKER_COMPOSE_HOST}
     volumes:
       - ~/tmp/openwhisk/invoker/logs:/logs
       - /var/run/docker.sock:/var/run/docker.sock