Fix Dockerfile reference URL in docs

docs/django.md

@@ -18,7 +18,7 @@ Let's set up the three files that'll get us started. First, our app is going to
     RUN pip install -r requirements.txt
     ADD . /code/
 
-That'll install our application inside an image with Python installed alongside all of our Python dependencies. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/use/builder/).
+That'll install our application inside an image with Python installed alongside all of our Python dependencies. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/reference/builder/).
 
 Second, we define our Python dependencies in a file called `requirements.txt`:
 

docs/index.md

@@ -99,7 +99,7 @@ Next, we want to create a Docker image containing all of our app's dependencies.
     WORKDIR /code
     RUN pip install -r requirements.txt
 
-This tells Docker to install Python, our code and our Python dependencies inside a Docker image. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/use/builder/).
+This tells Docker to install Python, our code and our Python dependencies inside a Docker image. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/reference/builder/).
 
 We then define a set of services using `fig.yml`:
 

docs/rails.md

@@ -18,7 +18,7 @@ Let's set up the three files that'll get us started. First, our app is going to
     RUN bundle install
     ADD . /myapp
 
-That'll put our application code inside an image with Ruby, Bundler and all our dependencies. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/use/builder/).
+That'll put our application code inside an image with Ruby, Bundler and all our dependencies. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/reference/builder/).
 
 Next, we have a bootstrap `Gemfile` which just loads Rails. It'll be overwritten in a moment by `rails new`.
 

docs/wordpress.md

@@ -17,7 +17,7 @@ FROM orchardup/php5
 ADD . /code
 ```
 
-This instructs Docker on how to build an image that contains PHP and Wordpress. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/use/builder/).
+This instructs Docker on how to build an image that contains PHP and Wordpress. For more information on how to write Dockerfiles, see the [Dockerfile tutorial](https://www.docker.io/learn/dockerfile/) and the [Dockerfile reference](http://docs.docker.io/en/latest/reference/builder/).
 
 Next up, `fig.yml` starts our web service and a separate MySQL instance: