Specify java version for compiler (#3)

* Specify java version for compiler

We use function `.getFirst()` and that was introduced in version 21

* Update java version in readme

---------

Co-authored-by: TeksuSiK <oskar@teksusik.pl>

Author: userMacieG

README.md

@@ -290,7 +290,7 @@ try {
 
 ## Requirements
 
-- Java 11 or higher
+- Java 21 or higher
 - Valid Kick.com application credentials
 
 ## Dependencies

build.gradle.kts

@@ -4,6 +4,12 @@ plugins {
     id("maven-publish")
 }
 
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(21))
+    }
+}
+
 group = "pl.teksusik"
 version = "1.0.1-SNAPSHOT"