Update ELK instructions

The slides didn't mention to clone the git repo containing
the Compose file for the ELK stack. This is now fixed.

Also, the version numbers were not all correctly set
in this Compose file. Also fixed.

elk/docker-compose.yml

@@ -2,14 +2,14 @@ version: "2"
 
 services:
   elasticsearch:
-    image: elasticsearch
+    image: elasticsearch:2
     # If you need to access ES directly, just uncomment those lines.
     #ports:
     #  - "9200:9200"
     #  - "9300:9300"
 
   logstash:
-    image: logstash
+    image: logstash:2
     command: |
       -e '
       input {
@@ -47,7 +47,7 @@ services:
       - "12201:12201/udp"
 
   kibana:
-    image: kibana
+    image: kibana:4
     ports:
       - "5601:5601"
     environment:

slides/containers/Logging.md

@@ -194,9 +194,13 @@ will have equal success with Fluent or other logging stacks!*
 
 - We are going to use a Compose file describing the ELK stack.
 
+- The Compose file is in the container.training repository on GitHub.
+
 ```bash
-$ cd ~/container.training/stacks
-$ docker-compose -f elk.yml up -d
+$ git clone https://github.com/jpetazzo/container.training
+$ cd container.training
+$ cd elk
+$ docker-compose up
 ```
 
 - Let's have a look at the Compose file while it's deploying.

stacks/elk.yml

@@ -5,7 +5,7 @@ services:
     image: elasticsearch:2
 
   logstash:
-    image: logstash
+    image: logstash:2
     command: |
       -e '
       input {