Enforce minimum Kotlin and Gradle versions in plugin

plugin/main/src/kotlinx/benchmark/gradle/BenchmarksPlugin.kt

@@ -30,17 +30,17 @@ class BenchmarksPlugin : Plugin<Project> {
         // DO NOT use properties of an extension immediately, it will not contain any user-specified data
         val extension = extensions.create(BENCHMARK_EXTENSION_NAME, BenchmarksExtension::class.java, project)
 
-        if (GradleVersion.current() < GradleVersion.version("5.1")) {
-            logger.error("JetBrains Gradle Benchmarks plugin requires Gradle version 5.1 or higher")
+        if (GradleVersion.current() < GradleVersion.version("6.8")) {
+            logger.error("JetBrains Gradle Benchmarks plugin requires Gradle version 6.8 or higher")
             return // TODO: Do we need to fail build at this point or just ignore benchmarks?
         }
 
         val kotlinClass = tryGetClass<KotlinBasePluginWrapper>("org.jetbrains.kotlin.gradle.plugin.KotlinBasePluginWrapper")
         if (kotlinClass != null) {
             plugins.findPlugin(kotlinClass)?.run {
                 logger.info("Detected Kotlin plugin version '$kotlinPluginVersion'")
-                if (VersionNumber.parse(kotlinPluginVersion) < VersionNumber(1, 3, 50, null))
-                    logger.error("JetBrains Gradle Benchmarks plugin requires Kotlin version 1.3.40 or higher")
+                if (VersionNumber.parse(kotlinPluginVersion) < VersionNumber(1, 4, 30, null))
+                    logger.error("JetBrains Gradle Benchmarks plugin requires Kotlin version 1.4.30 or higher")
             }
         }