fix the android packaging issue (#497)

java/build-android.gradle

@@ -84,6 +84,13 @@ android {
         }
     }
 
+    publishing {
+        singleVariant("release") {
+            withSourcesJar()
+            withJavadocJar()
+        }
+    }
+
 }
 
 task sourcesJar(type: Jar) {