timers.lua: fix arg1 as string

[TehZarathustra]

makes it possible to use this example. currently it doesn't work

-- A timer running every second that starts after 2 minutes regardless of pauses
Timers:CreateTimer("uniqueTimerString3", {
    useGameTime = false,
    endTime = 120,
    callback = function()
        print ("Hello. I'm running after 2 minutes and then every second thereafter.")
        return 1
    end
})