Add test for double underscore in layers

Author: asisayag2

cloudinary-core/src/test/java/com/cloudinary/transformation/LayerTest.java

@@ -64,6 +64,8 @@ public void testLayerOptions() {
         Object tests[] = {
                 new Layer().publicId("logo"),
                 "logo",
+                new Layer().publicId("logo__111"), //testing SNI-4729
+                "logo__111",
                 new Layer().publicId("folder/logo"),
                 "folder:logo",
                 new Layer().publicId("logo").type("private"),