update Java version in README

README.md

@@ -97,13 +97,13 @@ _P.S. The application that is tested in the course is quite complex and covers a
 
 Mandatory requirements:
 
-* Java 17 (JDK flavour (OpenJDK/Azul/Oracle) does not matter). For the correct Java version setup I can recommend [JEnv](https://www.youtube.com/watch?v=9FVZyeFDXo0) (Mac/Linux) and the [Maven Toolchains Plugin](https://maven.apache.org/plugins/maven-toolchains-plugin/toolchains/jdk.html) (Windows)
+* Java 21 (JDK flavour (OpenJDK/Azul/Oracle) does not matter). For the correct Java version setup I can recommend [JEnv](https://www.youtube.com/watch?v=9FVZyeFDXo0) (Mac/Linux) and the [Maven Toolchains Plugin](https://maven.apache.org/plugins/maven-toolchains-plugin/toolchains/jdk.html) (Windows)
 
 ```
 $ java -version
-openjdk version "17" 2021-09-14 LTS
-OpenJDK Runtime Environment Zulu17.28+13-CA (build 17+35-LTS)
-OpenJDK 64-Bit Server VM Zulu17.28+13-CA (build 17+35-LTS, mixed mode, sharing)
+openjdk version "21.0.1" 2023-10-17 LTS
+OpenJDK Runtime Environment Temurin-21.0.1+12 (build 21.0.1+12-LTS)
+OpenJDK 64-Bit Server VM Temurin-21.0.1+12 (build 21.0.1+12-LTS, mixed mode)
 ```
 
 * Docker Engine (Community Edition is enough) and Docker Compose: