Update docker readme

I meant to do this change but I've totally forgot about it :/

Sorry of the inconvenience.

Thanks.

Author: ahornace

docker/README.md

@@ -130,8 +130,7 @@ docker run -d \
 
 If you want to do your own development, you can build the image yourself:
 
-    ./mvnw -DskipTests=true clean package && \
-        docker build -t opengrok-dev .
+    docker build -t opengrok-dev .
 
 Then run the container: