Use source/target compatibility

`options.release` usage was banned by repo owners

Author: Lipen

build.gradle.kts

@@ -73,12 +73,8 @@ allprojects {
     tasks {
         withType<JavaCompile> {
             // See: https://docs.gradle.org/current/userguide/building_java_projects.html#sec:compiling_with_release
-            if (JavaVersion.current().isJava10Compatible) {
-                options.release = 8
-            } else {
-                sourceCompatibility = JavaVersion.VERSION_1_8.toString()
-                targetCompatibility = JavaVersion.VERSION_1_8.toString()
-            }
+            sourceCompatibility = JavaVersion.VERSION_1_8.toString()
+            targetCompatibility = JavaVersion.VERSION_1_8.toString()
             options.encoding = "UTF-8"
             options.compilerArgs.add("-Xlint:all")
         }