provisioner/shell: Added code formatting.

website/source/docs/provisioners/shell.html.markdown

@@ -148,7 +148,7 @@ on reboot or in your shell script. For example, on Gentoo:
 
 *My shell script doesn't work correctly on Ubuntu*
 
-* On Ubuntu the /bin/sh shell is
+* On Ubuntu the `/bin/sh` shell is
 [dash](http://en.wikipedia.org/wiki/Debian_Almquist_shell). If your script has
 [bash](http://en.wikipedia.org/wiki/Bash_(Unix_shell)) specific commands in it
 then put `#!/bin/bash` at the top of your script. Differences
@@ -156,12 +156,12 @@ between dash and bash can be found on the [DashAsBinSh](https://wiki.ubuntu.com/
 
 *My shell works when I login but fails with the shell provisioner*
 
-* See the above tip. More than likely your login shell is using /bin/bash
-while the provisioner is using /bin/sh.
+* See the above tip. More than likely your login shell is using `/bin/bash`
+while the provisioner is using `/bin/sh`.
 
 *My installs hang when using `apt-get` or `yum`*
 
-* Make sure you add a "-y" to the command to prevent it from requiring
+* Make sure you add a `-y` to the command to prevent it from requiring
 user input before proceeding.
 
 *How do I tell what my shell script is doing?*