awesomeWM: rename the current tag

awesome-rename-tag.rc.lua

    -- Rename tag
    awful.key({ modkey, "Shift",  }, "F2",    function ()
                        awful.prompt.run({ prompt = "Rename tab: ", text = awful.tag.selected().name, },
                        mypromptbox[mouse.screen].widget,
                        function (s)
                            awful.tag.selected().name = s
                        end)
                end),

awful.screen.focused().mypromptbox.widget instead of mypromptbox[mouse.screen].widget worked for me