build.gradle: Update Kotlin version to 1.3.40.

It's needed for @Parcelize.

build.gradle

 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
-    ext.kotlin_version = '1.3.31'
+    ext.kotlin_version = '1.3.40'
     repositories {
         google()
         jcenter()