Use $IMAGE_NAME instead of "this"

Pablo Chico de Guzman · Pablo Chico de Guzman · commit c4277fcc3bf5 · 2016-02-18T18:58:33.000+01:00
diff --git a/docker-compose.test.yml b/docker-compose.test.yml
@@ -1,5 +1,5 @@
 sut:
-  image: this
+  image: $IMAGE_NAME
   links:
     - redis
   command: echo "Test pass!"
