osx/csrutil.md: update placeholder

- https://github.com/command-line-interface-pages/prototypes/pull/32

pages/osx/csrutil.md

@@ -21,7 +21,7 @@
 
 - Add an IPv4 address to the list of allowed NetBoot sources:
 
-`csrutil netboot add {{ip_address}}`
+`csrutil netboot add {{ip}}`
 
 - Reset the System Integrity Protection status and clear the NetBoot list: