Upgrading to Kotlin 1.4.20, most recent version supported by Gradle 6.9.2

Author: vetler

mockito-kotlin/build.gradle

@@ -3,7 +3,7 @@ apply from: '../gradle/publishing.gradle'
 apply plugin: 'org.jetbrains.dokka'
 
 buildscript {
-    ext.kotlin_version = "1.3.50"
+    ext.kotlin_version = "1.4.20"
 
     repositories {
         mavenCentral()

tests/build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = System.getenv("KOTLIN_VERSION") ?: '1.3.50'
+    ext.kotlin_version = System.getenv("KOTLIN_VERSION") ?: '1.4.20'
     println "$project uses Kotlin $kotlin_version"
 
     repositories {