chore(preview-sidebar): update flow-typed for new bp icons

Author: Jose Gaston

flow-typed/npm/@box/blueprint-web-assets_vx.x.x.js

@@ -9,6 +9,10 @@ declare module '@box/blueprint-web-assets/icons/Medium' {
   declare export var XMark: React$ComponentType<any>;
   declare export var Comment: React$ComponentType<any>;
   declare export var Metadata: React$ComponentType<any>;
+  declare export var ChevronDown: React$ComponentType<any>;
+  declare export var ChevronUp: React$ComponentType<any>;
+  declare export var RightSidebarChevronClose: React$ComponentType<any>;
+  declare export var RightSidebarChevronOpen: React$ComponentType<any>;
 }
 
 declare module '@box/blueprint-web-assets/icons/MediumFilled' {