urclock second hand is not precise

[Andrei Korshikov]

I started several instances (less than 5) of urclock and noticed that
second hands for some of them are not in sync. I.e. I can always find
a couple of windows with following behaviour:

1. Window A moves second hand, Window B keeps second hand stopped.
2. Window A keeps second hand stopped, Window B moves.
3. Repeat indefinitely.

So, there is about 0.5 sec noticeable delay.

I use Arch Linux, i3 window manager, and no custom compiler flags.

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Andrei Korshikov