small typo. fixed broken code snippet

Docker-DCO-1.1-Signed-off-by: Nathan Hsieh <hsieh.nathan@gmail.com> (github: nhsiehgit)

docs/sources/userguide/usingdocker.md

@@ -114,8 +114,8 @@ We've specified an image: `training/webapp`. This image is a
 pre-built image we've created that contains a simple Python Flask web
 application.
 
-Lastly, we've specified a command for our container to run: `python
-app.py`. This launches our web application.
+Lastly, we've specified a command for our container to run: `python app.py`. 
+This launches our web application.
 
 > **Note:** 
 > You can see more detail on the `docker run` command in the [command