Bug#822231: xfce4-terminal: Fira Code font not displayed correctly

[Egmont Koblinger]

This was fixed in libvte-2.91-0 version 0.52 (combined with
xfce4-terminal 0.8.x).

(Upstream bug: https://bugzilla.gnome.org/show_bug.cgi?id=793391.)

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