message: Fixed return type on addSlide method
diff: @@ -82,7 +82,7 @@ declare class PptxGenJS {
  * @param {string} masterSlideName - Master Slide name
  * @returns {ISlide} the new Slide
  */
  - addSlide(masterSlideName?: string): PptxGenJS.ISlide
  + addSlide(masterSlideName?: string): PptxGenJS.Slide
  /**
  * Create a custom Slide Layout in any size
  * @param {IUserLayout} layout - an object with user-defined w/h
  