Bump kotlin-gradle-plugin from 1.3.72 to 1.5.31

Bumps [kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.3.72 to 1.5.31.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -11,7 +11,7 @@ buildscript {
         kbox = { "ch.tutteli.kbox:kbox:$kbox_version" }
         niokVersion = '1.4.7'
         niok = { "ch.tutteli.niok:niok:$niokVersion" }
-        kotlin_version = '1.3.72'
+        kotlin_version = '1.5.31'
 
         // test
         jacocoToolVersion = '0.8.7'