Fix widget.wibox.slider example

[Cyan903]

The provided example for widget.wibox.slider does not work due to naughty.notify requiring the message to be a string.

local widget = wibox.widget {
    bar_shape           = gears.shape.rounded_rect,
    bar_height          = 3,
    bar_color           = beautiful.border_color,
    handle_color        = beautiful.bg_normal,
    handle_shape        = gears.shape.circle,
    handle_border_color = beautiful.border_color,
    handle_border_width = 1,
    value               = 25,
    widget              = wibox.widget.slider,
}

-- Connect to `property::value` to use the value on change
widget:connect_signal("property::value", function(_, new_value)
    naughty.notify { title = "Slider changed", message = new_value }
end)

new_value returns a number in this case. Running this code will throw an error in lib/naughty/widget/_markup.lua:

awesome/lib/naughty/widget/_markup.lua

Line 25 in 8b1f895

text = text:gsub(pattern, subs)