message: total time = decay + predelay
  summing instead of subtracting fixes potential range issues when preDelay is larger than decay
  fixes
diff: @@ -80,8 +80,8 @@ Tone.Reverb.prototype.generate = function(){
  gainNode.gain.setValueAtTime(0, 0);
  gainNode.gain.setValueAtTime(1, this.preDelay);
  //decay
  - gainNode.gain.exponentialApproachValueAtTime(0, this.preDelay, this.decay - this.preDelay);
  - }.bind(this), this.decay).then(function(buffer){
  + gainNode.gain.exponentialApproachValueAtTime(0, this.preDelay, this.decay + this.preDelay);
  + }.bind(this), this.decay + this.preDelay).then(function(buffer){
  this._convolver.buffer = buffer.get();
  return this;
  }.bind(this));
  