Update Changelog to add #13.

Author: suikan4github

CHANGELOG.md

@@ -5,6 +5,7 @@ History of the project development
 The issue #16 changes its public member function. But it is referred internally from ::rpp_driver::Adau1361 class. Not called by user program. Then, the major version number is not needed to change. 
 
 ### Added
+- [Issue #13](https://github.com/suikan4github/rpp_driver/issues/13)  Exclude Mock definition from the GCov coverage. 
 ### Changed
 - [Issue #10](https://github.com/suikan4github/rpp_driver/issues/10) Cover APIs of the Raspberry Pi Pico SDK.
 - [Issue #16](https://github.com/suikan4github/rpp_driver/issues/16)  Change the member function name from ConfigureSRC() to ConfigureSrc().