fix(gradle): clean up the sub-project build directory

Author: lxcmyf

build.gradle

@@ -82,3 +82,11 @@ task copyToParent(type: Copy) {
 
 build.finalizedBy(copyToParent)
 
+gradle.buildFinished {
+    if (project.hasProperty('cleanSubBuild')) {
+        subprojects {
+            buildDir.deleteDir()
+        }
+    }
+}
+