tweak test

Author: solkimicreb

README.md

@@ -568,7 +568,7 @@ Instead of returning an object, you should directly mutate the received stores.
 
 #### Beginner
 
-* [Clock Widget](https://solkimicreb.github.io/react-easy-state/examples/clock/build) ([source](/examples/clock/)) ([codesandbox](https://codesandbox.io/s/github/solkimicreb/react-easy-state/tree/master/examples/clock)): a reusable clock widget with a tiny local state store.
+* [Clock Widget](https://solkimicreb.github.io/react-easy-state/examples/clock/build) ([source](/examples/clock/)) ([codesandbox](https://codesandbox.io/s/github/solkimicreb/react-easy-state/tree/master/examples/clock)) ([react-native](/examples/native-clock/)): a reusable clock widget with a tiny local state store.
 * [Stopwatch](https://solkimicreb.github.io/react-easy-state/examples/stop-watch/build) ([source](/examples/stop-watch/)) ([codesandbox](https://codesandbox.io/s/github/solkimicreb/react-easy-state/tree/master/examples/stop-watch)) ([tutorial](https://hackernoon.com/introducing-react-easy-state-1210a156fa16)): a stopwatch with a mix of normal and computed state properties.
 
 #### Advanced

babel.config.js

@@ -15,7 +15,7 @@ const test = {
 }
 
 const bundle = process.env.BUNDLE
-if (bundle.indexOf('es5') !== -1) {
+if (bundle && bundle.indexOf('es5') !== -1) {
   test.presets.push('@babel/preset-env')
 }