Fix typo

Author: Dallas62

README.md

@@ -296,7 +296,7 @@ PushNotification.localNotification({
   smallIcon: "ic_notification", // (optional) default: "ic_notification" with fallback for "ic_launcher"
   bigText: "My big text that will be shown when notification is expanded", // (optional) default: "message" prop
   subText: "This is a subText", // (optional) default: none
-  bigPictureUl: "https://www.example.tld/picture.jpg", // (optional) default: undefined
+  bigPictureUrl: "https://www.example.tld/picture.jpg", // (optional) default: undefined
   color: "red", // (optional) default: system default
   vibrate: true, // (optional) default: true
   vibration: 300, // vibration length in milliseconds, ignored if vibrate=false, default: 1000