Update description of rebase permission

Nowadays the button to rebase a change is called 'REBASE'.

Release-Notes: skip
Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: Ibcc538aa7be9dfdd48ddb37aa96795e730cb95e5

Documentation/access-control.txt

diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index 185fa07..31c3536 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -782,7 +782,7 @@
 === Rebase
 
 This category permits users to rebase changes via the web UI by pushing
-the `Rebase Change` button.
+the `REBASE` button.
 
 The change owner and submitters can always rebase changes in the web UI
 (even without having the `Rebase` access right assigned).