chore(deps): bump kotlin_version in /tutorials/kotlin/Polygons (googlemaps-samples#273)

Author: dependabot-preview[bot]

tutorials/kotlin/Polygons/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 = '1.3.72'
+    ext.kotlin_version = '1.4.0'
     repositories {
         jcenter()
         google()