Updating tutorial to apache dockerhub image

Author: machristie

docs/tutorial/custom_ui_tutorial.md

@@ -599,7 +599,7 @@ the settings_local.py file for local development. Move or copy it to the
     2. Run the following to create a Docker container called **custom-ui-tutorial**.
 
             cd $HOME/custom_ui_tutorial_app
-            docker run --pull always -d --name custom-ui-tutorial -p 8000:8000 -v "${PWD}:/extensions" -v "${PWD}/settings_local.py:/code/django_airavata/settings_local.py" machristie/airavata-django-portal
+            docker run --pull always -d --name custom-ui-tutorial -p 8000:8000 -v "${PWD}:/extensions" -v "${PWD}/settings_local.py:/code/django_airavata/settings_local.py" apache/airavata-django-portal
     3. Wait until the Docker container starts up. Go to <http://localhost:8000>
     and when it loads and you see **Welcome to your new Wagtail site!**, then
     you're ready to proceed to the next step.