External deps: update Rarian

[Don Scorgie <Don Scorgie org>]

Hi,

I've just released Rarian 0.6.0 and would like to update the external
dependence for GNOME to this.

Current version (minimum and recommended): 0.5.8
Suggested version: 0.6.0

Reasons: 
GNOME bug #474556 [1]
Fixes various other minor problems

As suggested by the version number, this is the final release in this
series.  Future work (excluding bug fixes) will begin in the 0.7 branch.

Thanks
Don

[1] http://bugzilla.gnome.org/show_bug.cgi?id=474556