put the item <3> at the end of the line

It is necessary to generate correctly the book.

Author: aollier

book/06-github/sections/2-contributing.asc

@@ -71,9 +71,9 @@ $ cd blink
 $ git checkout -b slow-blink <2>
 Switched to a new branch 'slow-blink'
 
-$ sed -i '' 's/1000/3000/' blink.ino <3> (MacOSX)
+$ sed -i '' 's/1000/3000/' blink.ino (MacOSX) <3>
 # If you're on a Linux system, do this instead:
-# $ sed -i 's/1000/3000/' blink.ino
+# $ sed -i 's/1000/3000/' blink.ino <3>
 
 $ git diff --word-diff <4>
 diff --git a/blink.ino b/blink.ino