Fix UniqueGiftBackdrop json fields (#1541)

* Fix UniqueGiftBackdrop NAME_FIELD

* Fix UniqueGiftBackdrop COLORS_FIELD and RARITY_PER_MILLE_FIELD

Author: denisklebanovich

telegrambots-meta/src/main/java/org/telegram/telegrambots/meta/api/objects/gifts/UniqueGiftBackdrop.java

@@ -31,9 +31,9 @@
 @JsonIgnoreProperties(ignoreUnknown = true)
 @JsonInclude(JsonInclude.Include.NON_NULL)
 public class UniqueGiftBackdrop implements BotApiObject {
-    private static final String NAME_FIELD = "center_color";
-    private static final String COLORS_FIELD = "edge_color";
-    private static final String RARITY_PER_MILLE_FIELD = "symbol_color";
+    private static final String NAME_FIELD = "name";
+    private static final String COLORS_FIELD = "colors";
+    private static final String RARITY_PER_MILLE_FIELD = "rarity_per_mille";
 
     /**
      * Name of the backdrop