Bump kernel version due to incompatible changes.

Update Kotlin language version to 1.6.0.

Author: ileasile

build.gradle.kts

@@ -74,6 +74,7 @@ dependencies {
 buildSettings {
     withLanguageLevel(rootSettings.kotlinLanguageLevel)
     withCompilerArgs {
+        requiresOptIn()
         skipPrereleaseCheck()
         samConversionsClass()
     }

gradle.properties

@@ -1,7 +1,7 @@
-baseVersion=0.10.3
+baseVersion=0.11.0
 
-kotlinLanguageLevel=1.5
-stableKotlinLanguageLevel=1.5
+kotlinLanguageLevel=1.6
+stableKotlinLanguageLevel=1.6
 jvmTarget=1.8
 
 kotlin.jupyter.add.api=false

src/main/kotlin/org/jetbrains/kotlinx/jupyter/message_types.kt

@@ -592,13 +592,11 @@ object ScriptDiagnosticSerializer : KSerializer<ScriptDiagnostic> {
 
 object MessageDataSerializer : KSerializer<MessageData> {
     @InternalSerializationApi
-    private val contentSerializers = MessageType.values()
-        .map { it.type to it.contentClass.serializer() }
-        .toMap()
+    private val contentSerializers = MessageType.values().associate { it.type to it.contentClass.serializer() }
 
     override val descriptor: SerialDescriptor = serializer<JsonObject>().descriptor
 
-    @InternalSerializationApi
+    @OptIn(InternalSerializationApi::class)
     override fun deserialize(decoder: Decoder): MessageData {
         require(decoder is JsonDecoder)
         val element = decoder.decodeJsonElement().jsonObject