message: requiring BufferSource
diff: -define(["Tone/core/Tone", "Tone/source/Source", "Tone/core/Buffer"], function (Tone) {
  +define(["Tone/core/Tone", "Tone/source/Source", "Tone/core/Buffer", "Tone/source/BufferSource"], function (Tone) {
  /**
  * @class Tone.GrainPlayer implements [granular synthesis](https://en.wikipedia.org/wiki/Granular_synthesis).
  