Bump kotlin-gradle-plugin from 1.4.10 to 1.4.20 (#593)

Bumps [kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.4.10 to 1.4.20.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.4.20/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.4.10...v1.4.20)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

build.gradle

@@ -21,7 +21,7 @@ import org.springframework.boot.gradle.plugin.SpringBootPlugin
 
 buildscript {
     ext {
-        kotlin_version = '1.4.10'
+        kotlin_version = '1.4.20'
         spring_boot_version = '2.3.5.RELEASE'
     }