Step 4: Integration Testing the Environment requires user to run `docker rm db` first

This is for your blog entry `http://www.dwmkerr.com/learn-docker-by-building-a-microservice/`

I was following the tutorial but ran into a bug for step 4 when running the command `docker run --name db test-database`

I received a `docker: Error response from daemon: Conflict. The name "/db" is already ...`

Running `docker rm db` first fixed this issue. Perhaps add a note to step 4?