chore: fix npm badge

Author: Q1w1N

README.md

@@ -67,4 +67,4 @@ react-native-fast-shimmer is an open source project and will always remain free
 [license-badge]: https://img.shields.io/npm/l/react-native-fast-shimmer?style=for-the-badge
 [license]: https://github.com/callstack/react-native-fast-shimmer/blob/main/LICENSE
 [npm-url]: https://npmjs.com/package/react-native-fast-shimmer
-[npm]: https://img.shields.io/npm/v/react-native-fast-shimmer?style=flat-square
+[npm]: https://img.shields.io/npm/v/react-native-fast-shimmer?style=for-the-badge