[Contributing] Replace HEAD~3 by upstream/master

lemoinem · lemoinem · commit c0de1cb392b4 · 2014-01-07T08:53:16.000-05:00
As per @cordoval suggestion: symfony#3421 (comment)
diff --git a/contributing/code/patches.rst b/contributing/code/patches.rst
@@ -382,7 +382,7 @@ convert many commits to one commit. To do this, use the rebase command:
 
 .. code-block:: bash
 
-    $ git rebase -i HEAD~3
+    $ git rebase -i upstream/master
     $ git push -f origin BRANCH_NAME
 
 The number 3 here must equal the amount of commits in your branch. After you
