Update README.md typo issue on billmock

Author: pmnxis

README.md

@@ -1279,7 +1279,7 @@ Work in progress crates. Help the authors make these crates awesome!
 - [Booster](https://github.com/quartiq/booster): Firmware for an RF power amplifier, including telemetry via MQTT and run-time configuration
 - [Thermostat EEM](https://github.com/quartiq/thermostat-eem): Firmware for a multi-channel temperature controller used in physics experiments
 - [Card/IO ECG](https://github.com/card-io-ecg/card-io-fw): Firmware for a business-card sized ECG device with Wifi connectivity
-- [BillMcok](https://github.com/pmnxis/billmock-app-rs): Firmware for credit card terminal add-on hardware to install on Korean arcade machines
+- [BillMock](https://github.com/pmnxis/billmock-app-rs): Firmware for credit card terminal add-on hardware to install on Korean arcade machines
 
 ## Old books, blogs and training materials