Updated attributes.asc source block to use diff highlighting

Author: crd

book/08-customizing-git/sections/attributes.asc

@@ -121,7 +121,7 @@ $ git config diff.exif.textconv exiftool
 
 If you replace an image in your project and run `git diff`, you see something like this:
 
-[source,console]
+[source,diff]
 ----
 $ diff --git a/image.png b/image.png
 index 88839c4..4afcb7c 100644