Update obsolete command line argument

--set-upstream-to is the replacement for --set-upstream

Author: owen-jones-gen

book/05-distributed-git/sections/contributing.asc

@@ -412,7 +412,7 @@ To jessica@githost:simplegit.git
 
 This is called a _refspec_.
 See <<_refspec>> for a more detailed discussion of Git refspecs and different things you can do with them.
-Also notice the `-u` flag; this is short for `--set-upstream`, which configures the branches for easier pushing and pulling later.
+Also notice the `-u` flag; this is short for `--set-upstream-to`, which configures the branches for easier pushing and pulling later.
 
 Next, John emails Jessica to say he's pushed some changes to the `featureA` branch and asks her to verify them.
 She runs a `git fetch` to pull down those changes: