corrected a typo

README.md

 # Spatial Coverage Sampling and Random Sampling from Compact Geographical Strata
 
-Since 2019, `spcosa` has been a formal R-package. As such, it is directly available from the Comprehensive R Archive Network (CRAN). 
+Since 2009, `spcosa` has been a formal R-package. As such, it is directly available from the Comprehensive R Archive Network (CRAN). 
 
 See https://CRAN.R-project.org/package=spcosa for more information.
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