Also produce Java 8 byte code for objectbox-kotlin.

Author: greenrobot-team

objectbox-kotlin/build.gradle

@@ -23,6 +23,13 @@ apply plugin: 'org.jetbrains.dokka'
 sourceCompatibility = JavaVersion.VERSION_1_8
 targetCompatibility = JavaVersion.VERSION_1_8
 
+// Produce Java 8 byte code, would default to Java 6.
+tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+}
+
 dokka {
     outputFormat = 'html'
     outputDirectory = javadocDir