Update Kotlin version from 1.9.20 to 1.6.0 in build.gradle file. #216 (#217)

Author: rosuH

build.gradle

@@ -1,7 +1,7 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
-    ext.kotlin_version="1.9.20"
+    ext.kotlin_version="1.6.0"
     repositories {
         google()
         mavenCentral()