Log Message:
Updated abcm2ps to 8.13.7.

---- Version 8.13.7 - 2017-02-26 ----

Don't display beams when no visible note with a stem
	(reported by Gerhard Schacherl)
Fix non working !ped! and !ped-up! with SVG output
	(reported by Gerhard Schacherl)
Fix non working "%%pos stem hidden"
	(reported by Gerhard Schacherl)
Fix bad horizontal spacing since 8.13.6
	(reported by David Lacroix)
Fix clash of slurs with note decorations since 8.13.6
	(reported by David Lacroix)