Migrate back to Kotlin

lib/build.gradle.kts

@@ -1,8 +1,8 @@
-plugins {
-    // Apply the scala Plugin to add support for Scala.
-    scala
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
+plugins {
+    kotlin("jvm") version "1.4.10"
 
-    // Apply the java-library plugin for API and implementation separation.
     `java-library`
 }
 
@@ -10,27 +10,15 @@ group = "tribufu"
 version = "0.0.1"
 
 repositories {
-    // Use Maven Central for resolving dependencies.
     mavenCentral()
 }
 
 dependencies {
-    // Use Scala 2.13 in our library project
-    implementation("org.scala-lang:scala-library:2.13.3")
+    testImplementation(kotlin("test-junit"))
+}
 
-    // This dependency is used internally, and not exposed to consumers on their own compile classpath.
-    implementation("com.google.guava:guava:30.0-jre")
-
-    // Use Scalatest for testing our library
-    testImplementation("junit:junit:4.13.1")
-    testImplementation("org.scalatest:scalatest_2.13:3.2.3")
-    testImplementation("org.scalatestplus:junit-4-13_2.13:3.2.2.0")
-
-    // Need scala-xml at test runtime
-    testRuntimeOnly("org.scala-lang.modules:scala-xml_2.13:1.2.0")
-
-    // This dependency is exported to consumers, that is to say found on their compile classpath.
-    api("org.apache.commons:commons-math3:3.6.1")
+tasks.test {
+    useJUnit()
 }
 
 tasks.jar {
@@ -38,3 +26,7 @@ tasks.jar {
         attributes(mapOf("Implementation-Title" to project.name, "Implementation-Version" to project.version))
     }
 }
+
+tasks.withType<KotlinCompile>() {
+    kotlinOptions.jvmTarget = "1.8"
+}