Fix typo

Author: khoih-prog

README.md

@@ -6,7 +6,7 @@
 [![contributions welcome](https://img.shields.io/badge/contributions-welcome-brightgreen.svg?style=flat)](#Contributing)
 [![GitHub issues](https://img.shields.io/github/issues/khoih-prog/NRF52_MBED_TimerInterrupt.svg)](http://github.com/khoih-prog/NRF52_MBED_TimerInterrupt/issues)
 
-<a href="https://www.buymeacoffee.com/khoihprog6" target="_blank"><img src="https://cdn.buymeacoffee.com/buttons/v2/default-yellow.png" alt="Buy Me A Coffee" style="height: 60px !important;width: 181px !important;" ></a>
+<a href="https://www.buymeacoffee.com/khoihprog6" target="_blank"><img src="https://cdn.buymeacoffee.com/buttons/v2/default-yellow.png" alt="Buy Me A Coffee" style="height: 50px !important;width: 181px !important;" ></a>
 
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