Move sr latin po for gnome-user-docs.

[Jiro Matsuzawa <jmatsuzawa src gnome org>]

Hi Serbian translation team,

The sr latin po for gnome-user-docs does not exist in the sr@latin directory.
The po exists in sr direcotry instead.
It seems to cause building gnome-user-docs to fail.
As far as I know, just to git mv sr/sr latin po sr@latin/sr latin po
will fix the problem.
Would you fix it?
See Bug 672618 [1].

I thank you very much in advance for your cooperation.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=672618

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Jiro Matsuzawa
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