Update README.md

Author: sirdarckcat

README.md

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 # Google CTF
 
-This repository lists most of the challenges used in the Google CTF since 2017, as well as most of the infrastructure that can be used to run them. **IMPORTANT** - The code in the 2017, 2018, 2019, 2020 and 2021 folders has unfixed security vulnerabilities. These are there on purpose, and running these on real production infrastructure is not safe.
+This repository lists most of the challenges used in the Google CTF since 2017, as well as most of the infrastructure that can be used to run them. **IMPORTANT** - The code in the 201x and 202x folders have unfixed security vulnerabilities. These are there on purpose, and running these on real production infrastructure is not safe.
 
 Read more about the Google CTF here: https://security.googleblog.com/2017/06/announcing-google-capture-flag-2017.html