Bump kotlin_version from 1.4.10 to 1.4.21-2

Bumps `kotlin_version` from 1.4.10 to 1.4.21-2.

Updates `kotlin-gradle-plugin` from 1.4.10 to 1.4.21-2

Updates `kotlin-stdlib-jdk8` from 1.4.10 to 1.4.21-2
- [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)

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

Author: dependabot-preview[bot]

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.4.10'
+    ext.kotlin_version = '1.4.21-2'
     repositories {
         jcenter()
         maven {