Fix a index for @{u} and @{upstream} in remote-branches.asc

Author: srgizh

book/03-git-branching/sections/remote-branches.asc

@@ -179,7 +179,7 @@ Branch serverfix set up to track remote branch serverfix from origin.
 .Upstream shorthand
 ====
 When you have a tracking branch set up, you can reference its upstream branch with the `@{upstream}` or `@{u}` shorthand.
-So if you're on the `master` branch and it's tracking `origin/master`, you can say something like `git merge @{u}` instead of `git merge origin/master` if you wish.(((+++@{u}+++)))(((+++@{upstream}+++)))
+So if you're on the `master` branch and it's tracking `origin/master`, you can say something like `git merge @{u}` instead of `git merge origin/master` if you wish.(((@{u})))(((@{upstream})))
 ====
 
 If you want to see what tracking branches you have set up, you can use the `-vv` option to `git branch`.