Fix warnings in build.gradle

...and add a default task

Author: Andy Coates

build.gradle

@@ -81,15 +81,16 @@ test {
     }
 }
 
-task createClasspathManifest {
-    File outputDir = file("$buildDir/$name")
+tasks.register('createClasspathManifest') {
+    var outputFile = layout.buildDirectory.file("$name/plugin-classpath.txt")
 
     inputs.files sourceSets.main.runtimeClasspath
-    outputs.dir outputDir
+    outputs.file outputFile
 
     doLast {
-        outputDir.mkdirs()
-        file("$outputDir/plugin-classpath.txt").text = sourceSets.main.runtimeClasspath.join('\n')
+        File file = outputFile.get().asFile
+        file.parentFile.mkdirs()
+        file.text = sourceSets.main.runtimeClasspath.join('\n')
     }
 }
 
@@ -114,10 +115,12 @@ gradlePlugin {
 
 publishing { // used for publishing to local maven repository
     publications {
-        pluginMaven(MavenPublication) {
+        create("pluginMaven", MavenPublication) {
             groupId = 'org.javamodularity'
             artifactId = 'moduleplugin'
             version = project.version
         }
     }
 }
+
+defaultTasks("check")