readme: use coinbase link

README.md

@@ -21,7 +21,7 @@ If you find this image useful here's how you can help:
 
 - Send a Pull Request with your awesome new features and bug fixes
 - Help new users with [Issues](https://github.com/sameersbn/docker-browser-bundle/issues) they may encounter
-- Send me a tip on [Gittip](https://gittip.com/sameersbn/) or using Bitcoin at **16rDxVqJPyYAFYPLduTaSiwe7ZiY1hHqKM**
+- Send me a tip via [Bitcoin](https://www.coinbase.com/sameersbn) or using [Gratipay](https://gratipay.com/sameersbn/)
 
 # Installation