Fix #695, fix black background when closing SwipebackActivity with Animations or Transitions

Author: YoKeyword

fragmentation_swipeback/src/main/java/me/yokeyword/fragmentation_swipeback/core/SwipeBackActivityDelegate.java

@@ -58,7 +58,7 @@ public boolean swipeBackPriority() {
 
     private void onActivityCreate() {
         mActivity.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
-        mActivity.getWindow().getDecorView().setBackgroundDrawable(null);
+        mActivity.getWindow().getDecorView().setBackgroundColor(Color.TRANSPARENT);
         mSwipeBackLayout = new SwipeBackLayout(mActivity);
         ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
         mSwipeBackLayout.setLayoutParams(params);