Prep Release v2.3.0 (#91)

* v2.3.0
* Add overscan count prop

Author: jameskerr

packages/react-arborist/package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-arborist",
-  "version": "2.2.0",
+  "version": "2.3.0",
   "license": "MIT",
   "source": "src/index.ts",
   "main": "dist/index.js",

packages/showcase/pages/cities.tsx

@@ -46,6 +46,7 @@ export default function Cities() {
                 padding={15}
                 rowHeight={30}
                 indent={15}
+                overscanCount={8}
                 onSelect={(selected) => setSelectedCount(selected.length)}
                 onActivate={(node) => setActive(node.data)}
                 onFocus={(node) => setFocused(node.data)}