Fix remaining errors in stem.js
Fix remaining errors in stem.js

Silverwolf90/vexflow,Huji/vexflow,Huji/vexflow,Huji/vexflow,Tails/vexflow,Silverwolf90/vexflow,Silverwolf90/vexflow,Tails/vexflow,Tails/vexflow,aaronmars/vexflow,aaronmars/vexflow,aaronmars/vexflow