Remove usage of internal Gradle API (#548)

Gradle tasks should be subtypes of DefaultTask, not the internal `ConventionTask`

Author: adam-enko

atomicfu-gradle-plugin/api/atomicfu-gradle-plugin.api

@@ -18,7 +18,7 @@ public final class kotlinx/atomicfu/plugin/gradle/AtomicFUPluginExtension {
 	public final fun setVerbose (Z)V
 }
 
-public abstract class kotlinx/atomicfu/plugin/gradle/AtomicFUTransformTask : org/gradle/api/internal/ConventionTask {
+public abstract class kotlinx/atomicfu/plugin/gradle/AtomicFUTransformTask : org/gradle/api/DefaultTask {
 	public field classPath Lorg/gradle/api/file/FileCollection;
 	public field inputFiles Lorg/gradle/api/file/FileCollection;
 	public fun <init> ()V

atomicfu-gradle-plugin/src/main/kotlin/kotlinx/atomicfu/plugin/gradle/AtomicFUGradlePlugin.kt

@@ -7,7 +7,6 @@ package kotlinx.atomicfu.plugin.gradle
 import kotlinx.atomicfu.transformer.*
 import org.gradle.api.*
 import org.gradle.api.file.*
-import org.gradle.api.internal.*
 import org.gradle.api.provider.Provider
 import org.gradle.api.provider.ProviderFactory
 import org.gradle.api.tasks.*
@@ -451,7 +450,7 @@ class AtomicFUPluginExtension(pluginVersion: String?) {
 }
 
 @CacheableTask
-abstract class AtomicFUTransformTask : ConventionTask() {
+abstract class AtomicFUTransformTask : DefaultTask() {
     @get:Inject
     internal abstract val providerFactory: ProviderFactory