Upgrade to Kotlin 1.3.60

Closes gh-24006

build.gradle

@@ -7,7 +7,7 @@ buildscript {
 
 plugins {
 	id 'io.spring.dependency-management' version '1.0.8.RELEASE' apply false
-	id 'org.jetbrains.kotlin.jvm' version '1.3.50' apply false
+	id 'org.jetbrains.kotlin.jvm' version '1.3.60' apply false
 	id 'org.jetbrains.dokka' version '0.9.18' apply false
 	id 'org.asciidoctor.convert' version '1.5.8'
 	id 'io.spring.nohttp' version '0.0.3.RELEASE'
@@ -48,7 +48,7 @@ configure(allprojects) { project ->
 			mavenBom "io.projectreactor:reactor-bom:Dysprosium-SR1"
 			mavenBom "io.rsocket:rsocket-bom:1.0.0-RC5"
 			mavenBom "org.eclipse.jetty:jetty-bom:9.4.21.v20190926"
-			mavenBom "org.jetbrains.kotlin:kotlin-bom:1.3.50"
+			mavenBom "org.jetbrains.kotlin:kotlin-bom:1.3.60"
 			mavenBom "org.jetbrains.kotlinx:kotlinx-coroutines-bom:1.3.2"
 			mavenBom "org.junit:junit-bom:5.5.2"
 		}