Upgrade Kotlin to 1.6.20

Resolves:
#163

Author: joffrey-bion

api/chrome-devtools-kotlin.api

@@ -10265,7 +10265,7 @@ public final class org/hildan/chrome/devtools/domains/dom/DOMAttributes : java/u
 	public final fun containsValue (Ljava/lang/Object;)Z
 	public fun containsValue (Ljava/lang/String;)Z
 	public final fun entrySet ()Ljava/util/Set;
-	public synthetic fun get (Ljava/lang/Object;)Ljava/lang/Object;
+	public final synthetic fun get (Ljava/lang/Object;)Ljava/lang/Object;
 	public final fun get (Ljava/lang/Object;)Ljava/lang/String;
 	public fun get (Ljava/lang/String;)Ljava/lang/String;
 	public final fun getAction ()Ljava/lang/String;

build.gradle.kts

@@ -1,5 +1,5 @@
 plugins {
-    val kotlinVersion = "1.6.10"
+    val kotlinVersion = "1.6.20"
     kotlin("jvm") version kotlinVersion
     kotlin("plugin.serialization") version kotlinVersion
     id("org.jetbrains.dokka") version "1.6.10"