misc/androidstudio/src/main/groovy/org/golang/mobile: update gobind path

Gobind now outputs Java sources to the java/ subdirectory. Update the
gradle plugin to match. Only projects using reverse bindings are
affected.

Change-Id: Id7f893d3c67a9ab63336c4e031c9196a0b6dad2c
Reviewed-on: https://go-review.googlesource.com/99775
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

misc/androidstudio/src/main/groovy/org/golang/mobile/GobindPlugin.groovy

@@ -80,7 +80,7 @@ class GobindPlugin implements Plugin<Project> {
 		bindTask.bootClasspath = variant.javaCompile.options.bootClasspath
 		// TODO: Detect when updating the Java classes is redundant.
 		bindTask.outputs.upToDateWhen { false }
-		variant.registerJavaGeneratingTask(bindTask, outputDir)
+		variant.registerJavaGeneratingTask(bindTask, new File(outputDir, "java"))
 		// Then, generate the JNI libraries with the gomobile tool.
 		Task libTask = project.tasks.create("gomobile${variant.name.capitalize()}", GomobileTask)
 		libTask.bootClasspath = variant.javaCompile.options.bootClasspath