left and right inputs of merger are explicitly mono
left and right inputs of merger are explicitly mono

this fixes issue of not splitting correctly in FF and Safari.

lukephills/Tone.js,BlokDust/Tone.js,BlokDust/Tone.js,Tonejs/Tone.js,lukephills/Tone.js,TONEnoTONE/Tone.js,Tonejs/Tone.js,TONEnoTONE/Tone.js