Update to Bach BWV 988 aria

(Steve Shorter)
        Bar 6: correct 2nd bass dotted quarter note, beat 2.5->beat 2
	Bar 18: correct e->g in last eight note in treble
(Javier Ruiz-Alma)
	update to v2.6.1
	minor cosmetics
	Bar 21: add prallup to first treble note
	Bar 23: add prallup to the 'a' in first voice
Close #12