git-gui: fix shortcut for menu "Commit/Revert Changes"

The shortcut was not properly recognized previously.
Signed-off-by: NHeiko Voigt <heiko.voigt@mahr.de>
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -3371,6 +3371,8 @@ bind .   <$M1B-Key-s> do_signoff
 bind .   <$M1B-Key-S> do_signoff
 bind .   <$M1B-Key-t> do_add_selection
 bind .   <$M1B-Key-T> do_add_selection
+bind .   <$M1B-Key-j> do_revert_selection
+bind .   <$M1B-Key-J> do_revert_selection
 bind .   <$M1B-Key-i> do_add_all
 bind .   <$M1B-Key-I> do_add_all
 bind .   <$M1B-Key-minus> {show_less_context;break}