Update kotlin -> 1.4.20 & java -> 15

.sdkmanrc

@@ -1,5 +1,5 @@
 # Enable auto-env through the sdkman_auto_env config
 # Add key=value pairs of SDKs to use below
-java=14.0.2-open
+java=15-open
-gradle=6.7
+gradle=6.8-rc-1
-kotlin=1.4.10
+kotlin=1.4.20

Dockerfile

@@ -1,4 +1,4 @@
-FROM openjdk:14-alpine as jdkbuilder
+FROM openjdk:15-alpine as jdkbuilder
 
 RUN apk add --no-cache binutils
 

buildSrc/build.gradle.kts

@@ -12,8 +12,8 @@ repositories {
 }
 
 dependencies {
-    implementation("org.jetbrains.kotlin:kotlin-gradle-plugin:1.4.10")
+    implementation("org.jetbrains.kotlin:kotlin-gradle-plugin:1.4.20")
-    implementation("org.jetbrains.kotlin:kotlin-serialization:1.4.10")
+    implementation("org.jetbrains.kotlin:kotlin-serialization:1.4.20")
     implementation("com.github.jengelman.gradle.plugins:shadow:6.1.0")
     implementation("org.jlleitschuh.gradle:ktlint-gradle:9.4.1")
     implementation("com.github.ben-manes:gradle-versions-plugin:0.28.0")

buildSrc/src/main/kotlin/be/simplenotes/java-convention.gradle.kts

@@ -16,8 +16,8 @@ group = "be.simplenotes"
 version = "1.0-SNAPSHOT"
 
 java {
-    sourceCompatibility = JavaVersion.VERSION_14
+    sourceCompatibility = JavaVersion.VERSION_15
-    targetCompatibility = JavaVersion.VERSION_14
+    targetCompatibility = JavaVersion.VERSION_15
 }
 
 tasks.withType<JavaCompile> {

buildSrc/src/main/kotlin/be/simplenotes/kotlin-convention.gradle.kts

@@ -8,12 +8,12 @@ plugins {
 
 dependencies {
     implementation(kotlin("stdlib-jdk8"))
-    implementation(platform("org.jetbrains.kotlin:kotlin-bom:1.4.10"))
+    implementation(platform("org.jetbrains.kotlin:kotlin-bom:1.4.20"))
 }
 
 tasks.withType<KotlinCompile> {
     kotlinOptions {
-        jvmTarget = "14"
+        jvmTarget = "15"
         javaParameters = true
         freeCompilerArgs = listOf(
             "-Xinline-classes",