Bump kotlin.version from 1.4.20 to 1.4.21

Bumps `kotlin.version` from 1.4.20 to 1.4.21.

Updates `kotlin-stdlib-jdk8` from 1.4.20 to 1.4.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.4.20...v1.4.21)

Updates `kotlin-reflect` from 1.4.20 to 1.4.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.4.20...v1.4.21)

Updates `kotlin-test` from 1.4.20 to 1.4.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.4.20...v1.4.21)

Updates `kotlin-maven-allopen` from 1.4.20 to 1.4.21

Updates `kotlin-maven-plugin` from 1.4.20 to 1.4.21

Signed-off-by: dependabot-preview[bot] <[email protected]>

pom.xml

@@ -39,7 +39,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 
         <!-- Compile -->
-        <kotlin.version>1.4.20</kotlin.version>
+        <kotlin.version>1.4.21</kotlin.version>
         <detekt.version>1.14.2</detekt.version>
         <jcommander.version>1.80</jcommander.version>
         <snakeyaml.version>1.21</snakeyaml.version>