Fix direction of slide transition (#330)

Defect since introduction of SlideSet in
49b1917

Author: philipphenkel

src/components/transitionable.js

@@ -35,9 +35,9 @@ const Transitionable = function (target) {
     },
 
     transitionDirection() {
-      const { slideIndex, lastSlide } = this.props;
+      const { slideIndex, lastSlideIndex } = this.props;
       const slide = this.context.store.getState().route.slide || 0;
-      return this.state.reverse ? slideIndex > slide : slideIndex > lastSlide;
+      return this.state.reverse ? slideIndex > slide : slideIndex > lastSlideIndex;
     },
 
     getTransitionStyles() {