branch doc: change `git branch <pattern>` to use `<branchname>`

Change an example for `git branch <pattern>` to say `git branch
<branchname>` to be consistent with the synopsis. This changes
documentation added in d8d33736b5 ("branch: allow pattern arguments",
2011-08-28).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -142,7 +142,7 @@ This option is only applicable in non-verbose mode.
 	List both remote-tracking branches and local branches.
 
 --list::
-	Activate the list mode. `git branch <pattern>` would try to create a branch,
+	Activate the list mode. `git branch <branchname>` would try to create a branch,
 	use `git branch --list <pattern>` to list matching branches.
 
 -v::