Merge pull request #960 from transloadit/fix/window-react-native

Fix @uppy/core window !== undefined check for React Native

packages/@uppy/core/src/index.js

@@ -785,7 +785,7 @@ class Uppy {
     })
 
     // show informer if offline
-    if (typeof window !== 'undefined') {
+    if (typeof window !== 'undefined' && window.addEventListener) {
       window.addEventListener('online', () => this.updateOnlineStatus())
       window.addEventListener('offline', () => this.updateOnlineStatus())
       setTimeout(() => this.updateOnlineStatus(), 3000)