fix typo (#194)

diff --git a/docker-compose/README.md b/docker-compose/README.md
index 30617f1..c0c3607 100644
--- a/docker-compose/README.md
+++ b/docker-compose/README.md
@@ -231,5 +231,5 @@
 ## Local Docker containers for controllers and invokers
 
 By default this setup uses published images for controller and invokers from `openwhisk` namespace i.e.
-`openwhisk/controller` and `openwhisk/invoker`. To make use of locally build images you can use `DOCKER_OW_IMAGE_PREFIX`
-variable i.e. `DOCKER_OW_IMAGE_PREFIX=whisk make quick-start`
+`openwhisk/controller` and `openwhisk/invoker`. To make use of locally build images you can use `DOCKER_IMAGE_PREFIX`
+variable i.e. `DOCKER_IMAGE_PREFIX=whisk make quick-start`