Update README.md

Author: Bin-Cao

README.md

@@ -46,7 +46,7 @@ If you are using this code, please cite:
 
      
 ## Update log / 日志
-Before version 2.1, function building
+Before version 2.0, function building
 
 Bgolearn V2.1.1 Jun 9, 2023. *para noise_std* By default, the built-in Gaussian process model estimates the noise of the input dataset by maximum likelihood, and yields in a more robust model.