Update Kotlin

* Just updated Kotlin to newest version

Author: molikuner

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.3.11'
+    ext.kotlin_version = '1.3.20'
     ext.dokka_version = '0.9.17'
 
     repositories { jcenter() }