Updated attributes.asc source block to remove shell prompt

Author: crd

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

@@ -123,7 +123,7 @@ If you replace an image in your project and run `git diff`, you see something li
 
 [source,diff]
 ----
-$ diff --git a/image.png b/image.png
+diff --git a/image.png b/image.png
 index 88839c4..4afcb7c 100644
 --- a/image.png
 +++ b/image.png