update code block formatting

_episodes/01-prep.md

@@ -75,7 +75,7 @@ CONTAINER ID        IMAGE               COMMAND             CREATED
 
 _NOTE: You can also use `sudo` without a password, but you probably will not need it in this session. For example,_
 
-``` bash
+``` shell
 [training@registry1-private ~]$ sudo /usr/bin/whoami
 root
 ```